Methods for use in oil and gas operations

ABSTRACT

Disclosed are compositions and methods for use in oil and gas operations.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to U.S. ProvisionalApplication No. 62/624,092, filed. Jan. 30, 2018, which is incorporatedby reference herein in its entirety.

BACKGROUND

Reservoir systems, such as petroleum reservoirs, typically containfluids such as water and a mixture of hydrocarbons such as oil and gas.To remove (“produce”) the hydrocarbons from the reservoir, differentmechanisms can be utilized such as primary, secondary or tertiaryrecovery processes.

In a primary recovery process, hydrocarbons are displaced from areservoir as a result of the high natural differential pressure betweenthe reservoir and the bottomhole pressure within a wellbore. Thereservoir's energy and natural forces drive the hydrocarbons containedin the reservoir into the production well and up to the surface.Artificial lift systems, such as sucker rod pumps, electricalsubmersible pumps or gas-lift systems, are often implemented in theprimary production stage to reduce the bottomhole pressure within thewell. Such systems increase the differential pressure between thereservoir and the wellbore intake; thus, increasing hydrocarbonproduction. However, even with use of such artificial lift systems onlya small fraction of the original-oil-in-place (OOIP) is typicallyrecovered using primary recovery processes as the reservoir pressure,and the differential pressure between the reservoir and the wellboreintake declines overtime due to production. For example, typically onlyabout 10-20% of the OOIP can be produced before primary recovery reachesits limit, either when the reservoir pressure is so low that theproduction rates are not economical or when the proportions of gas orwater in the production stream are too high.

In order to increase the production life of the reservoir, secondary ortertiary recovery processes can be used. Secondary recovery processesinclude water or gas well injection, while tertiary methods are based oninjecting additional chemical compounds into the well, such assurfactants and polymers. Typically in these processes, fluids areinjected into the reservoir to maintain reservoir pressure and drive thehydrocarbons to producing wells. An additional 10-50% of OOIP can beproduced in addition to the oil produced during primary recovery.

While secondary and tertiary methods of oil recovery can further enhanceoil production from a reservoir, care must be taken in choosing theright processes and chemicals for each reservoir, as some methods maycause formation damage or plugging. Damage can occur in the formationeven with the careful choice of chemicals during enhanced oil recoveryprocesses. The near wellbore area is especially prone to damage as it issubjected to higher concentrations of enhanced oil recovery chemicals,Additionally, water and steam flooding can cause fines migration whichmay eventually plug pores, while surfactant flooding can cause a buildupof polymers within the pores of the reservoir. Other near wellboredamage can include changes in wettability due to oil wet solids, such asthrough the buildup in the formation of asphaltenes and paraffin.

SUMMARY

Provided herein are concentrated surfactant compositions. The surfactantcompositions can be a liquid at ambient (room) temperature. Thesurfactant compositions can comprise a surfactant package in an amountof from 0.2% to 98% by weight, based on the total weight of thesurfactant composition; a co-solvent in an amount of from greater than0% to 95% by weight, based on the total weight of the surfactantcomposition, and a liquid polymer (LP) composition in an amount of from0.1% to 60% by weight, based on the total weight of the surfactantcomposition. The surfactant composition can have a total water contentof from 0.5% to 20% by weight, based on the total weight of thesurfactant composition.

In one example, the surfactant composition can comprise from 10% to 40%by weight, based on the total weight of the surfactant composition, of asurfactant package, wherein the surfactant package comprises one or moresurfactants chosen from an alkoxy sulfate surfactant TDA-8PO-Sulfate), aC10-C30 isomerized olefin sulfonate (e.g., a C20-28 isomerized olefinsulfonate, a C16-18 isomerized olefin sulfonate, or any combinationthereof), a sulfosuccinate (e.g., a dialkyl sulfosuccinate, such assodium dihexyl sulfosuccinate), an aryl sulfonate surfactant, or anycombination thereof; from 20% to 70% by weight, based on the totalweight of the surfactant composition, of a co-solvent (e.g., ethyleneglycol monobutyl ether, tri-ethylene glycol monobutyl ether, or anycombination thereof); and from 2% to 50% by weight, based on the totalweight of the surfactant composition, of an LP composition.

The concentrated surfactant compositions described herein can bedirectly diluted with an aqueous fluid (e.g., brine) to produce anaqueous surfactant-polymer solution having the desired concentration ofcomponents (e.g., the desired polymer concentration, the desiredsurfactant concentration, the desired co-solvent concentration, or anycombination thereof for a particular oil and gas operation) in a singlestep. Accordingly, also provided are methods for preparing aqueoussurfactant-polymer solutions that comprise combining a surfactantcomposition with an aqueous fluid in a single stage mixing process toprovide the aqueous surfactant-polymer solution, wherein the singlestage mixing process comprises applying a specific mixing energy of atleast 0.10 kJ/kg to the surfactant composition and the aqueous fluid;wherein the aqueous polymer solution comprises a polymer concentrationof from 50 to 15,000 ppm; and wherein the aqueous polymer solution has afilter ratio of 1.5 or less at 15 psi using a 1.2 μm filter.

Also provided are methods for preparing the concentrated liquidsurfactant compositions described herein. Methods for preparing theconcentrated liquid surfactant compositions can comprise combining an LPcomposition, a surfactant package, and a co-solvent to form thesurfactant composition. The surfactant package can comprise from 0.2% to98% by weight of the surfactant composition. The co-solvent can comprisefrom greater than 0% to 95% by weight of the surfactant composition. TheLP composition can comprise from 0.1% to 60% by weight of the surfactantcomposition. The surfactant composition can have a total water contentof from 0.5% to 20% by weight, based on the total weight of thesurfactant composition.

In some embodiments, combining the LP composition, the surfactantpackage, and the co-solvent can comprise mixing from 0.1 parts to 60parts of the LP composition with from 0.2 parts to 98 parts of thesurfactant composition and from greater than 0 parts to 95 parts of theco-solvent. In some embodiments, combining the LP composition, thesurfactant package, and the co-solvent can comprise adding the LPcomposition to a mixture comprising the surfactant package and theco-solvent.

Also provided are methods of using these aqueous surfactant-polymersolutions in a variety of oil and gas operations, including enhanced oilrecovery operations and/or wellbore remediation.

DESCRIPTION OF DRAWINGS

FIG. 1A is a photograph illustrating the appearance of concentratedsurfactant composition 1 prior to dilution.

FIG. 1B is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (3000 ppm polymer) prepared by dilution ofconcentrated surfactant composition 1 with brine in a single stagemixing process.

FIG. 2A is a photograph illustrating the appearance of concentratedsurfactant composition 2 prior to dilution.

FIG. 2B is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (3000 ppm polymer) at room temperatureprepared by dilution of concentrated surfactant composition 2 with brinein a single stage mixing process.

FIG. 2C is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (3000 ppm polymer) at reservoir temperatureprepared by dilution of concentrated surfactant composition 2 with brinein a single stage mixing process.

FIG. 3A is a photograph illustrating the appearance of concentratedsurfactant composition 3 prior to dilution.

FIG. 3B is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (2500 ppm polymer) at room temperatureprepared by dilution of concentrated surfactant composition 3 with brinein a single stage mixing process (3 minutes of mixing).

FIG. 3C is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (2500 ppm polymer) at reservoir temperatureprepared by dilution of concentrated surfactant composition 3 with brinein a single stage mixing process.

FIG. 4A is a photograph illustrating the appearance of concentratedsurfactant composition 4 prior to dilution.

FIG. 4B is a photograph illustrating the appearance of an aqueoussurfactant-polymer solution (300 ppm polymer) prepared by dilution ofconcentrated surfactant composition 4 with brine in a single stagemixing process.

FIG. 5 is a plot comparing the viscosity of surfactant composition 1 andthe liquid polymer (LP) composition present in the surfactantcomposition.

FIG. 6 shows the viscosity curves as a function of shear rate atreservoir temperature for three different aqueous surfactant-polymersolutions having different concentrations of polymer prepared bydilution of surfactant composition 1.

FIG. 7 is a residual oil recovery plot during injection of an aqueoussurfactant-polymer solution (2500 ppm polymer) as a cleanup solution insurrogate rock.

FIG. 8 is plot of krw and pressure drop (dp, in psi) during thedisplacement of residual oil during injection of an aqueoussurfactant-polymer solution (2500 ppm polymer) as a cleanup solution insurrogate rock.

FIG. 9 is a residual oil recovery plot during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer) as a cleanup solution inreservoir sand.

FIG. 10 is plot of krw and pressure drop (dp, in psi) during thedisplacement of residual oil during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer) as a cleanup solution inreservoir sand.

FIG. 11 is a photographic comparison of the reservoir sand before andafter the chemical cleanup flood.

FIG. 12 is a residual oil recovery plot during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer, prepared in run #2b2) asa cleanup solution in surrogate rock,

FIG. 13 is plot of krw and pressure drop (dp, in psi) during thedisplacement of residual oil during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer, prepared in run #2b2) asa cleanup solution in reservoir sand.

FIG. 14 is a residual oil recovery plot during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer, prepared in run #3a2) asa cleanup solution in surrogate rock.

FIG. 15 is plot of krw and pressure drop (dp, in psi) during thedisplacement of residual oil during injection of an aqueoussurfactant-polymer solution (3000 ppm polymer, prepared in run #3a2) asa cleanup solution in surrogate rock.

FIG. 16 is a photograph illustrating a cross section of the surrogaterock after the residual oil recovery aqueous surfactant-polymer solution(3000 ppm polymer, prepared in run #2b2) as a cleanup solution(corresponding to the recovery shown in FIG. 12 ). No significant oil isremaining following injection, as indicated by a clean core.

FIG. 17 is a photograph illustrating a cross section of the surrogaterock after the residual oil recovery aqueous surfactant-polymer solution(3000 ppm polymer, prepared in run #3a2) as a cleanup solution(corresponding to the recovery shown in FIG. 14 ). No significant oil isremaining following injection, as indicated by a clean core.

FIG. 18 is a process flow diagram schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises a single mixing step.

FIG. 19 is a process flow diagram schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises two mixing steps.

FIG. 20 is a process flow diagrams schematically illustrating an examplesingle stage mixing process for preparing an aqueous polymer solution.The example single stage mixing process comprises a plurality ofparallel mixing steps (e.g., parallel single mixing steps, parallelmultiple mixing steps, or a combination thereof).

FIGS. 21A and 21B are process flow diagrams schematically illustratingexample single stage mixing processes for preparing an aqueous polymersolution that comprise parallel single mixing steps carried out in apolymer mixing system (e.g., a subsea polymer mixing system).

FIGS. 22A and 22B are process flow diagrams schematically illustratingexample single stage mixing processes for preparing an aqueous polymersolution that comprise parallel multiple mixing steps carried out in apolymer mixing system (e.g., a subsea polymer mixing system).

DETAILED DESCRIPTION

The term “enhanced oil recovery” refers to techniques for increasing theamount of unrefined petroleum (e.g., crude oil) that may be extractedfrom an oil reservoir (e.g., an oil field). Using EOR, 40-60% of thereservoir's original oil can typically be extracted compared with only20-40% using primary and secondary recovery (e.g., by water injection ornatural gas injection). Enhanced oil recovery may also be referred to asimproved oil recovery or tertiary oil recovery (as opposed to primaryand secondary oil recovery). Examples of EOR operations include, forexample, miscible gas injection (which includes, for example, carbondioxide flooding), chemical injection (sometimes referred to as chemicalenhanced oil recovery (CEOR), and which includes, for example, polymerflooding, alkaline flooding, surfactant flooding, conformance controloperations, as well as combinations thereof such as alkaline-polymerflooding or alkaline-surfactant-polymer flooding), microbial injection,and thermal recovery (which includes, for example, cyclic steam, steamflooding, and fire flooding). In some embodiments, the EOR operation caninclude a polymer (P) flooding operation, an alkaline-polymer (AP)flooding operation, a surfactant-polymer (SP) flooding operation, analkaline-surfactant-polymer (ASP) flooding operation, a conformancecontrol operation, or any combination thereof. The terms “operation” and“application” may be used interchangeability herein, as in EORoperations or EOR applications.

For purposes of this disclosure, including the claims, the filter ratio(FR) can be determined using a 1.2 micron filter at 15 psi (plus orminus 10% of 15 psi) at ambient temperature (e.g., 25° C.). The 1.2micron filter can have a diameter of 47 mm or 90 mm, and the filterratio can be calculated as the ratio of the time for 180 to 200 ml ofthe inverted polymer solution to filter divided by the time for GO to 80ml of the inverted polymer solution to filter.

${FR} = \frac{{{\,^{t}200}\mspace{14mu}{ml}} - {{\,^{t}180}\mspace{14mu}{ml}}}{{{\,^{t}80}\mspace{14mu}{ml}} - {{\,^{t}60}\mspace{14mu}{ml}}}$For purposes of this disclosure, including the claims, the invertedpolymer solution is required to exhibit a FR of 1.5 or less.

The formation of aqueous surfactant-polymer solutions from a surfactantcomposition (e.g., by inversion of a surfactant composition comprising aLP composition such as an inverse emulsion polymer) can be challenging.For use in many applications, rapid and complete inversion of theinverse emulsion polymer composition is required. For example, for many,applications, rapid and continuous inversion and dissolution (e.g.,complete inversion and dissolution in five minutes or less) is required.For certain applications, including many oil and gas applications, itcan be desirable to completely form an aqueous surfactant-polymersolution (e.g., to invert and dissolve the surfactant compositioncomprising the emulsion or LP to a final concentration of from 500 to5000 ppm) in an in-line system in a short period of time (e.g., lessthan five minutes).

For certain applications, including many enhanced oil recovery (EOR)applications, it can be desirable that the aqueous surfactant-polymersolution flows through a hydrocarbon-bearing formation without pluggingthe formation. Plugging the formation can slow or inhibit oilproduction. This is an especially large concern in the case ofhydrocarbon-bearing formations that have a relatively low permeabilityprior to tertiary oil recovery.

One test commonly used to determine performance of an aqueoussurfactant-polymer solution in such conditions involves measuring thetime taken for given volumes/concentrations of solution to flow througha filter, commonly called a filtration quotient or Filter Ratio (“FR”).For example, U.S. Pat. No. 8,383,560 describes a filter ratio testmethod which measures the time taken by given volumes of a solutioncontaining 1000 ppm of active polymer to flow through a filter. Thesolution is contained in a cell pressurized to 2 bars and the filter hasa diameter of 47 mm and a pore size of 5 microns. The times required toobtain 100 ml (t100 ml), 200 ml (t200 ml), and 300 ml (t300 ml) offiltrate were measured. These values were used to calculate the FR,expressed by the formula below:

${FR} = \frac{{{\,^{t}300}\mspace{14mu}{ml}} - {{\,^{t}200}\mspace{14mu}{ml}}}{{{\,^{t}200}\mspace{14mu}{ml}} - {{\,^{t}100}\mspace{14mu}{ml}}}$

The FR generally represents the capacity of the polymer solution to plugthe filter for two equivalent consecutive volumes. Generally, a lower FRindicates better performance. U.S. Pat. No. 8,383,560, which isincorporated herein by reference, explains that a desirable FR usingthis method is less than 1.5.

However, polymer compositions that provide desirable results using thistest method, have not necessarily provided acceptable performance in thefield. In particular, many polymers that have an FR (using a 5 micronfilter) lower than 1.5 exhibit poor injectivity—i.e., when injected intoa formation, they tend to plug the formation, slowing or inhibiting oilproduction. A modified filter ratio test method using a smaller poresize (i.e., the same filter ratio test method except that the filterabove is replaced with a filter having a diameter of 47 mm and a poresize of 1.2 microns) and lower pressure (15 psi) provides a betterscreening method.

The methods described herein can produce aqueous surfactant-polymersolutions exhibiting a FR using the 1.2 micron filter of 1.5 or less viaefficient single stage mixing processes. In field testing, thesecompositions can exhibit improved injectivity overcommercially-available polymer compositions including other compositionshaving an FR (using a 5 micron filter) of less than 1.5. In someembodiments, injection of the aqueous surfactant-polymer solutionsdescribed herein in surrogate rock core having permeability of 1 Darcyor greater at a constant flowrate for at least 15 pore volumes yields astable pressure drop across the surrogate rock core. Procedures for suchmeasurements are described, for example, in SPE 179657 entitled“Permeability Reduction Due to use of Liquid Polymers and Development ofRemediation. Options” by Dwarakanath et al. (SPE ICER symposium inTulsa, Okla., 2016), and SPE 191391 entitled “Development of the MixingEnergy Concept to Hydrate Novel Liquid Polymers for Field Injection” byKim et al. (SPE Annual Technical Conference in Dallas, Tex., 2018), eachof which is incorporated herein by reference in its entirety. As such,the aqueous surfactant-polymer solutions prepared by the methodsdescribed herein are suitable for use in a variety of oil and gasapplications, including EOR.

In some embodiments, the compositions described herein can be analyzedusing the apparatus and methods described in U.S. Patent ApplicationPublication No. 2018/0031462 to Dwarakanath et al., which isincorporated herein by reference in its entirety.

Surfactant Compositions

Provided herein are liquid surfactant compositions. The liquidsurfactant compositions can comprise a surfactant package, a co-solvent,and a liquid polymer (LP) composition. The surfactant package can bepresent in the surfactant composition in an amount of from 0.2% to 98%by weight, based on the total weight of the surfactant composition. Theco-solvent can be present in the surfactant composition an amount offrom greater than 0% to 95% by weight, based on the total weight of thesurfactant composition. The LP composition can be present in thesurfactant composition in an amount of from 0.1% to 60% by weight, basedon the total weight of the surfactant composition. The surfactantcomposition can have a total water content (including the water presentin all components of the surfactant composition, of from 0.5% to 20% byweight, based on the total weight of the surfactant composition).

The concentrated surfactant composition can be directly diluted with anaqueous fluid (e.g., brine) to produce an aqueous surfactant-polymersolution having the desired concentration of components (e.g., thedesired polymer concentration, the desired surfactant concentration, thedesired co-solvent concentration, or any combination thereof for aparticular oil and gas operation) in a single step. This can eliminatethe need for multiple streams of individual components, therebyimproving process robustness. If desired, the aqueous surfactant-polymersolution can be continuously injected to remove near wellbore trappedoil or injected as a slug to mobilize residual oil in a tertiaryrecovery process. Such a process allows for rapid deployment ofsurfactant polymer flooding processes, especially in offshoreenvironments.

The surfactant compositions described herein can be quickly inverted,hydrated, and mixed in water under strong shear stress. Once diluted,the resulting aqueous surfactant-polymer solutions can exhibit superiorfilterability after a short hydration time. The surfactant compositionscan exhibit a comparable viscosity yield with conventional liquidpolymers. The resulting aqueous surfactant-polymer solutions alsoexhibit excellent performance in oil recovery applications.

In some cases, the surfactant compositions can have a greaterconcentration of surfactants and co-solvents than polymer. For example,the composition can have a total surfactant concentration equal to thesum of the weight percent concentration of all the surfactants presentin the surfactant composition and a total polymer concentration equal tothe sum of the weight percent concentration of all of the polymerspresent in the surfactant composition. In some embodiments, the weightratio of the total surfactant concentration to the total polymerconcentration can be at least 1:1 (e.g., at least 2:1, at least 3:1, atleast 4:1, at least 5:1, at least 6:1, or at least 7:1). In someembodiments, the weight ratio of the total surfactant concentration tothe total polymer concentration can be 8:1 or less (e.g., 7:1 or less,6:1 or less. 5:1 or less, 4:1 or less, 3:1 or less, or 2:1 or less).

The weight ratio of the total surfactant concentration to the totalpolymer concentration can range from any of the minimum values describedabove to any of the maximum values described above. For example, in someembodiments, the weight ratio of the total surfactant concentration tothe total polymer concentration in the surfactant composition can befrom greater that 1:1 to 8:1 (e.g., from 2:1 to 8:1, or from 3:1 to6:1).

The composition can also have a total co-solvent concentration equal tothe sum of the weight percent concentration of all the co-solventspresent in the surfactant composition and a total polymer concentrationequal to the sum of the weight percent concentration of all of thepolymers present in the surfactant composition. In some embodiments, theweight ratio of the total co-solvent concentration to the total polymerconcentration can be at least 1:1 (e.g., at least 2:1, at least 3:1, atleast 4:1, at least 5:1, at least 6:1, or at least 7:1). In someembodiments, the weight ratio of the total co-solvent concentration tothe total polymer concentration can be 8:1 or less (e.g., 7:1 or less,6:1 or less, 5:1 or less, 4:1 or less, 3:1 or less, or 2:1 or less).

The weight ratio of the total co-solvent concentration to the totalpolymer concentration can range from any of the minimum values describedabove to any of the maximum values described above. For example, in someembodiments, the weight ratio of the total co-solvent so concentrationto the total polymer concentration in the surfactant composition can befrom greater that 1:1 to 8:1 (e.g., from 2:1 to 8:1, or from 3:1 to6:1).

In some embodiments, the composition can have a total additiveconcentration equal to the sum of the weight percent concentration ofall the surfactants and all the co-solvents present in the surfactantcomposition, and a total polymer concentration equal to the sum of theweight percent concentration of all the polymers present in thesurfactant composition. In some embodiments, the weight ratio of thetotal additive concentration to the total polymer concentration can beat least 1:1 (e.g., at least 2:1, at least 3:1, at least 4:1, at least5:1, at least 6:1, or at least 7:1). In some embodiments, the weightratio of the total additive concentration to the total polymerconcentration can be 8:1 or less (e.g., 7:1 or less, 6:1 or less, 5:1 orless, 4:1 or less, 3:1 or less, or 2:1 or less).

The weight ratio of the total additive concentration to the totalpolymer concentration can range from any of the minimum values describedabove to any of the maximum values described above. For example, in someembodiments, the weight ratio of the total additive concentration to thetotal polymer concentration in the surfactant composition can be from1:1 to 8:1 (e.g., from 2:1 to 8:1, or from 3:1 to 6:1).

Surfactant Package

As discussed above, the surfactant compositions described herein caninclude a surfactant package comprising one or more surfactants.

In some embodiments, the surfactant package can be present in thesurfactant composition in an amount of at least 0.2% by weight (e.g., atleast 0.3% by weight, at least 0.4% by weight, at least 0.5% by weight,at least 0.6% by weight, at least 0.7% by weight, at least 0.8% byweight, at least 0.9% by weight, at least 1% by weight, at least 2% byweight, at least 3% by weight, at least 4% by weight, at least 5% byweight, at least 10% by weight, at least 15% by weight, at least 20% byweight, at least 25% by weight, at least 30% by weight, at least 35% byweight, at least 40% by weight, at least 45% by weight, at least 50% byweight, at least 55% by weight, at least 60% by weight, at least 65% byweight, at least 70% by weight, at least 75% by weight, at least 80% byweight, at least 85% by weight, at least 90% by weight, or at least 95%by weight), based on the total weight of the surfactant composition. Insome embodiments, the surfactant package can be present in thesurfactant composition in an amount of 98% by weight or less (e.g., 95%by weight or less, 90% by weight or less, 85% by weight or less, 80% byweight or less, 75% by weight or less, 70% by weight or less, 65% byweight or less, 60% by weight or less, 55% by weight or less, 50% byweight or less, 45% by weight or less, 40% by weight or less, 35% byweight or less, 30% by weight or less, 25% by weight or less, 20% byweight or less, 15% by weight or less, 10% by weight or less, 5% byweight or less, 4% by weight or less, 3% by weight or less, 2% by weightor less, 1% by weight or less, 0.9% by weight or less, 0.8% by weight orless, 0.7% by weight or less, 0.6% by weight or less, 0.5% by weight orless, 0.4% by weight or less, or 0.3% by weight or less), based on thetotal weight of the surfactant composition.

The surfactant package can be present in the surfactant composition inan amount ranging from any of the minimum values described above to anyof the maximum values described above. For example, in some embodiments,the surfactant package can be present in the surfactant composition inan amount of from 0.2% to 98% by weight (e.g., from 0.5% to 98% byweight, from 0.5% to 95% by weight, from 5% to 98% by weight, from 10%to 95% by weight, from 10% to 75% by weight, from 10% to 60% by weight,from 10% to 50% by weight, or from 10% to 40% by weight), based on thetotal weight of the surfactant composition.

In some embodiments, the surfactant package can comprise one or moreanionic surfactants. In some embodiments, the surfactant package canconsist essentially of one or more anionic surfactants. In someembodiments, the surfactant package can consist of one or more anionicsurfactants. In some embodiments, the surfactant package can compriseone or more anionic surfactants, one or more non-ionic surfactants, orany combination thereof. In some embodiments, the surfactant package canconsist essentially of one or more anionic surfactants, one or morenon-ionic surfactants, or any combination thereof. In some embodiments,the surfactant package can consist of one or more anionic surfactants,one or more non-ionic surfactants, or any combination thereof.

The surfactants can be any surfactants suitable for use in oil and gasoperations. For example, in some cases, the surfactant package cancomprise an anionic surfactant. The anionic surfactant can be, forexample, an anionic surfactant which comprises between 6 and 52 carbonatoms, for example, between 6 and 15, 16 and 30, 31 and 45, 46 and 52, 6and 25, 26 and 52, 6 and 15, 16 and 25, 26 and 35, and 36 and 45 carbonatoms. The hydrophobic (lipophilic) carbon tail may be a straight chain,branched chain, and/or may comprise cyclic structures. The hydrophobiccarbon tail may comprise single bonds, double bonds, triple bounds, orcombinations thereof. The hydrophilic side of the anionic surfactant cancomprise a sulfate, a sulfonate, two sulfonates, or a carboxylate, forexample. In embodiments, the anionic surfactant can comprise be a mix ofsurfactants with different length hydrophobic chain lengths. Inembodiments, the anionic surfactant can be, for example, a disulfonate,alkyldiphenyloxide disulfonate, mono alkyldiphenyloxide disulfonate,dialkyldiphenyloxide disulfonate, or a dialkyldiphenyloxidemonosulfonate, where the alkyl chain can be C1-C30 near or branched. Inembodiments, the anionic surfactant can be an alkylbenzene sulfonate ora dibenzene disulfonate. In specific embodiments, the anionic surfactantcan be benzenesulfonic acid, decyl(Sulfophenoxy)-disodium salt; linearor branched C1-C36 Alkyl:PO(0-65):EO (0-100) sulfate; or linear orbranched C1-C36 Alkyl:PO(0-65):EO (0-100) carboxylate. In embodiments,the anionic surfactant can be an isomerized olefin sulfonate (C6-C30),internal olefin sulfonate (C6-C30) or internal olefin disulfonate(C6-C30). In some embodiments, the anionic surfactant can be GuerbetPO(0-65) and EO (0-100) Sulfate (Guerbet portion can be C6-C36). In someembodiments, the anionic surfactant can be alkyl PO(0-65) and EO (0-100)Sulfonate: where the alkyl group is linear or branched C1-C36. In someembodiments, the anionic surfactant can be alpha olefin sulfonate(C6-C30), alkyl benzene sulfonate where the alkyl group is linear orbranched C6-C36, Guerbet PO(0-65) and EO (0-100) carboxylate (Guerbetcan be C6-C36). In some embodiments, the anionic surfactant can be asulfosuccinate (e.g., a dialkyl sulfosuccinate, such as sodium dihexylsulfosuccinate). In some embodiments, the surfactant package cancomprise a mixture of one or more different types of anionicsurfactants.

In some embodiments, the surfactant package can comprise one or moreinternal olefin sulfonates. As used herein, “internal olefin sulfonates”or “IOS” refers to an unsaturated hydrocarbon compound comprising atleast one carbon-carbon double bond and at least one SO₄ ⁻ group, or asalt thereof. In certain embodiments, the surfactant package cancomprise a C20-C28 internal olefin sulfonate. As used herein, a “C20-C28internal olefin sulfonate” or “C20-C28 IOS” refers to an IOS, or amixture of IOSs with an average carbon number of 20 to 28, or of 23 to25. The C20-C28 MS may comprise at least 80% of IOS with carbon numbersof 20 to 28, at least 90% of IOS with carbon numbers of 20 to 28, or atleast 99% of IOS with carbon numbers of 20 to 28. In certainembodiments, the surfactant package can comprise a C15-C18 internalolefin sulfonate. As used herein, a “C15-C18 internal olefin sulfonate”or “C15-C18 IOS” refers to an IOS or a mixture of IOSs with an averagecarbon number of 15 to 18, or of 16 to 17. The C15-C18 IOS may compriseat least 80% of IOS with carbon numbers of 15 to 18, at least 90% of IOSwith carbon numbers of 15 to 18, or at least 99% of IOS with carbonnumbers of 15 to 18. The internal olefin sulfonates may be alpha olefinsulfonates, such as an isomerized alpha olefin sulfonate. The internalolefin sulfonates may also comprise branching. The IOS may comprise atleast 20% branching, 30% branching, 40% branching, 50% branching, 60%branching, and 65% branching. In some embodiments, the branching isbetween 20-98%, 30-90%, 40-80%, or around 65%. Examples of internalolefin sulfonates and the methods to make them are found in U.S. Pat.No. 5,488,148, U.S. Patent Application Publication 2009/0112014, and SPE129766, all incorporated herein by reference.

In some embodiments, the surfactant package can comprise one or morealcohol alkoxylated sulfates. Alcohol alkoxylated sulfates can have thegeneral structure of alcohol-PO/EO-SO₄ ⁻, or a salt thereof. The alcoholgroup can comprise 10-32 carbon atoms (e.g., from 16 to 32, from 13 to17, or from 10 to 13 carbon atoms). The PO/EO group comprises 0-50ethylene oxide groups, 0-50 propylene oxide groups, or any combinationthereof. The alcohol alkoxylated sulfate may be the salt of the alcoholalkoxylated sulfate, such as a sodium alcohol alkoxylated sulfate. Insome examples, the alcohol alkoxylated sulfate can be atridecyl-8(propylene oxide)-sulfate (TDA-8(PO)—SO₄ ⁻), a TDA-4(PO)—SO₄⁻, a TDA-12(PO)—SO₄, or any combination thereof.

In some embodiments, the surfactant package can comprise one or morealcohol alkoxylated carboxylates. Alcohol alkoxylated carboxylates canhave the general structure of alcohol-PO/EO-COO⁻, or a salt thereof. Thealcohol group can comprise 10-32 carbon atoms (e.g., from 16 to 32, from13 to 17, or from 10 to 13 carbon atoms). The PO/EO group can comprise0-50 ethylene oxide groups, 0-50 propylene oxide groups, or anycombination thereof. In some examples, the alcohol alkoxylatedcarboxylate can be a C28-35PO-10EO-COO⁻ or a salt thereof.

In some embodiments, the surfactant package can comprise one or moresulfosuccinates. As used herein, “sulfosuccinate” refers to a chemicalhaving the structure:

or a salt thereof, wherein R₁ is a branched or unbranched carbon chaincomprising 5 to 7 carbon atoms and wherein R₂ is a branched orunbranched carbon chain comprising 5 to 7 carbon atoms. In some cases,the sulfosuccinate can be a sulfosuccinate salt, such as a sodiumsulfosuccinate. In certain embodiments, the sulfosuccinate can be sodiumdihexyl sulfosuccinate, which is considered a food grade,environmentally friendly compound. The dihexyl sulfosuccinate can havethe chemical structure shown below.

In some cases, the surfactant package can comprise a non-ionicsurfactant. Non-ionic surfactants can be included in the surfactantpackage to, for example, increase wettability. Examples of non-ionicsurfactants include, for example, alkylaryl alkoxy alcohols, alkylalkoxy, alcohols, and any combinations thereof. In embodiments, the HLBof the non-ionic surfactant can be greater than 10. Non-ionicsurfactants satisfying the above guidelines generally have the followingcharacteristics. The lipophilic moiety (tail) is an alkyl chain withtypically between 6 and 30 carbons, with or without an aromatic ring(phenyl) attached to it. This chain may be linear or branched. In someembodiments, branched lipophilic tails are derived from Guerbetalcohols. In embodiments, the non-ionic surfactant may be a mix ofsurfactants with different length lipophilic tail chain lengths. Forexample, the non-ionic surfactant may be C9-C:11:9EO, which indicates amixture of non-ionic surfactants that have a lipophilic tail length of 9carbon to 11 carbon, which is followed by a chain of 9 EOs. Thehydrophylic moiety is an ethoxy (EO) and/or propoxy (PO) chain with morethan two repeating units of EO and/or PO. In some embodiments, 1-100repeating units of EO are present. In some embodiments, 0-65 repeatingunits of PO are present. For example, the non-ionic surfactant couldcomprise 10EO:5PO or 5EO. In embodiments, the non-ionic surfactant maybe a mix of surfactants with different length lipophilic tail chainlengths. For example, the non-ionic surfactant may be C9-C11:PO9:EO2,which indicates a mixture of non-ionic surfactants that have alipophilic tail length of 9 carbon to 11 carbon, which is followed by achain of 9 POs and 2 EOs. In specific embodiments, the non-ionicsurfactant is linear C9-C11:9EO. In some embodiments, the non-ionicsurfactant is a Guerbet PO(0-65) and EO (0-100) (Guerbet can be C6-C36);or alkyl PO(0-65) and EO (0-100): where the alkyl group is linear orbranched C1-C36. In some embodiments it may be alkyl polyglucosides.

Suitable surfactants and combinations of surfactants are also described,for example, in U.S. Pat. No. 8,163,678 to Campbell et al.; U.S. Pat.No. 9,752,071 to Dwarakanath et al., and U.S. Pat. No. 7,770,641 toDwarakanath et al., U.S. Pat. No. 8,283,491 to Campbell et al., U.S.Pat. No. 8,573,299 to Dwarakanath et al., U.S. Pat. No. 8,993,798 toCampbell et at, U.S. Pat. No. 10,011,757 to Dwarakanath et at, U.S. Pat.No. 9,976,072 to Shong et al., U.S. Pat. No. 8,211,837 to Weerasooriyaet al., U.S. Pat. No. 9,896,617 to Dwarakanath et al, U.S. Pat. No.9,909,053 to Dwarakanath et al., U.S. Pat. No. 9,902,894 to Dwarakanathet al., U.S. Pat. No. 9,902,895 to Dwarakanath et al., U.S. Pat. No.9,422,469 to Dwarakanath et al., U.S. Pat. No. 9,605,198 to Dwarakanathet al., U.S. Pat. No. 9,617,464 to Dwarakanath et al., U.S. PatentApplication Publication No. 2017/0198202 to Shong et al., and U.S. Ser.No. 16/259,247 to Shong et al., all of which are incorporated herein byreference in their entirety.

In some embodiments, the surfactant package can comprise a primarysurfactant and one or more secondary co-surfactants. The primarysurfactant can comprise an anionic surfactant. For example, the primarysurfactant can comprise an anionic surfactant is chosen from an alkoxycarboxylate surfactant, an alkoxy sulfate surfactant, an alkoxysulfonate surfactant, an alkyl sulfonate surfactant, an aryl sulfonatesurfactant, an olefin sulfonate surfactant, a sulfosuccinate, or anycombination thereof. In certain embodiments, the primary surfactant cancomprise a C10-00 isomerized olefin sulfonate, a C8-C30 alkyl benzenesulfonate (ABS), or any combination thereof. In certain embodiments, theprimary surfactant can comprise a sulfosuccinate (e.g., a dialkylsulfosuccinate, such as sodium dihexyl sulfosuccinate). The one or moresecondary co-surfactants comprise an anionic surfactant, a non-ionicsurfactant, or any combination thereof. For example, in someembodiments, the one or more secondary co-surfactants are chosen from analkoxy carboxylate surfactant, an alkoxy sulfate surfactant, an alkoxysulfonate surfactant, an alkyl sulfonate surfactant, an aryl sulfonatesurfactant, an olefin sulfonate surfactant, a sulfosuccinate, or anycombination thereof.

In some of these embodiments, the primary surfactant can be present inan amount of from 1% to 40% by weight (e.g., from 5% to 25% by weight,from 8% to 20% by weight, or from 10% to 20% by weight), based on thetotal weight of the surfactant composition.

In some of these embodiments, the one or more secondary co-surfactantscan be present in an amount of from 0.2% to 25% by weight (e.g., from 1%to 20% by weight, from 8% to 20% by weight, or from 10% to 20% byweight), based on the total weight of the surfactant composition.

Co-Solvents

As discussed above, the surfactant compositions described herein caninclude one or more co-solvents.

In some embodiments; the co-solvent can be present in the surfactantcomposition in an amount greater than 0% by weight (e.g., at least 0.05%by weight, at least 0.1% by weight, at least 0.2% by weight; at least0.3% by weight, at least 0.4% by weight, at least 0.5% by weight; atleast 0.6% by weight, at least 0.7% by weight, at least 0.8% by weight,at least 0.9% by weight, at least 1% by weight, at least 2% by weight,at least 3% by weight, at least 4% by weight, at least 5% by weight, atleast 10% by weight, at least 15% by weight, at least 20% by weight, atleast 25% by weight, at least 30% by weight, at least 35% by weight, atleast 40% by weight, at least 45% by weight, at least 50% by weight, atleast 55% by weight, at least 60% by weight, at least 65% by weight, atleast 70% by weight, at least 75% by weight, at least 80% by weight, atleast 85% by weight, or at least 90% by weight), based on the totalweight of the surfactant composition. In some embodiments, theco-solvent can be present in the surfactant composition in an amount of95% by weight or less (e.g., 90% by weight or less, 85% by weight orless, 80% by weight or less. 75% by weight or less, 70% by weight orless, 65% by weight or less, 60% by weight or less, 55% by weight orless, 50% by weight or less, 45% by weight or less, 40% by weight orless, 35% by weight or less, 30% by weight or less, 25% by weight orless, 20% by weight or less, 15% by weight or less, 10% by weight orless, 5% by weight or less, 4% by weight or less, 3% by weight or less,2% by weight or less, 1% by weight or less, 0.9% by weight or less, 0.8%by weight or less, 0.7% by weight or less, 0.6% by weight or less, 0.5%by weight or less, 0.4% by weight or less, 0.3% by weight or less; 0.2%by weight or less, 0.1% by weight or less, or 0.05% by weight or less),based on the total weight of the surfactant composition.

The co-solvent can be present in the surfactant composition in an amountranging from any of the minimum values described above to any of themaximum values described above. For example, in some embodiments, theco-solvent can be present in the surfactant composition in an amount offrom greater than 0% to 95% by weight (e.g., from 0.2% to 95% by weight,from 0.5% to 95% by weight, from 5% to 95% by weight, from 10% to 95% byweight, from 10% to 75% by weight, from 10% to 60% by weight, from 10%to 50% by weight, from 20% to 50% by weight, or from 10% to 40% byweight), based on the total weight of the surfactant composition.

The co-solvent can comprise any co-solvent(s) suitable for use in oiland gas operations. Suitable co-solvents include, for example, alcohols,such as lower carbon chain alcohols such as isopropyl alcohol, ethanol,n-propyl alcohol, n-butyl alcohol, sec-butyl alcohol, n-amyl alcohol,sec-amyl alcohol, n-hexyl alcohol, sec-hexyl alcohol and the like;alcohol ethers, polyalkylene alcohol ethers, polyalkylene glycols,poly(oxyalkylene)glycols, poly(oxyalkylene)glycol ethers, ethoxylatedphenol, or any other common organic co-solvent or combinations of anytwo or more co-solvents. In one embodiment, the co-solvent is alkylethoxylate (C1-C6)-XEO X=1-30-linear or branched.

In some embodiments, the co-solvent can be chosen from a C1-C6 alcohol,an alcohol ether, a polyalkylene alcohol ether, a polyalkylene glycol, apoly(oxyalkylene)glycol, a poly(oxyalkylene)glycol ether, an ethoxylatedphenol, or any combination thereof.

LP Compositions

The surfactant compositions described herein can include any suitable LPcomposition. Herein, the term “liquid polymer (LP) composition” is usedto broadly refer to polymer compositions that are pumpable and/orflowable, so as to be compatible with the single stage mixing processesdescribed herein, Appropriate LP compositions can be selected forincorporation into the surfactant compositions in view of the desiredend use for the diluted surfactant composition.

In some embodiments, the LP composition can be present in the surfactantcomposition in an amount of at least 0.1% by weight (e.g., at least 0.2%by weight, at least 0.3% by weight, at least 0.4% by weight, at least0.5% by weight, at least 0.6% by weight, at least 0.7% by weight, atleast 0.8% by weight, at least 0.9% by weight, at least 1% by weight, atleast 2% by weight, at least 3% by weight, at least 4% by weight, atleast 5% by weight, at least 10% by weight, at least 15% by weight, atleast 20% by weight, at least 25% by weight, at least 30% by weight, atleast 35% by weight, at least 40% by weight, at least 45% by weight, atleast 50% by weight, or at least 55% by weight), based on the totalweight of the surfactant composition. In some embodiments, the LPcomposition can be present in the surfactant composition in an amount of60% by weight or less (e.g., 55% by weight or less, 50% by weight orless, 45% by weight or less, 40% by weight or less, 35% by weight orless, 30% by weight or less, 25% by weight or less, 20% by weight orless, 15% by weight or less, 10% by weight or less, 5% by weight orless, 4% by weight or less, 3% by weight or less, 2% by weight or less,1% by weight or less, 0.9% by weight or less, 0.8% by weight or less,0.7% by weight or less, 0.6% by weight or less, 0.5% by weight or less,0.4% by weight or less, 0.3% by weight or less, or 0.2% by weight orless), based on the total weight of the surfactant composition.

The LP composition can be present in the surfactant composition in anamount ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can be present in the surfactant composition in anamount of from 0.1% to 60% by weight (e.g., from 0.2% to 60% by weight,from 0.1% to 50% by weight, from 0.2% to 60% by weight, from 0.2% to 50%by weight, from 1% to 60% by weight, from 1% to 50% by weight, from 1%to 40% by weight, from 1% to 30% by weight, from 5% to 60% by weight,from 5% to 50% by weight, from 5% to 40% by weight, from 5% to 30% byweight, from 5% to 20% by weight, from 10% to 60% by weight, from 10% to50% by weight, from 10% to 40% by weight, from 10% to 30% by weight, orfrom 10% to 20% by weight), based on the total weight of the surfactantcomposition.

In some examples, the LP composition can comprise a substantiallyanhydrous polymer suspension that comprises a powder polymer having anaverage molecular weight of 0.5 to 30 million Daltons suspended in acarrier having an HLB of greater than or equal to 8. In these polymersuspensions, the powder polymer and the carrier can be present in thesubstantially anhydrous polymer suspension at a weight ratio of from20:80 to 80:20 (e.g., at a weight ratio of from 30:70 to 70:30, or at aweight ratio of from 40:60 to 60:40). The carrier can comprise at leastone surfactant. In some cases, the carrier can be water soluble. In somecases, the carrier can be water soluble and oil soluble.

LP compositions of this type are known in the art, and are discussed inmore detailed in the following cases having Chevron U.S.A. Inc. as anassignee: U.S. Patent Application Publication Nos, 2016/0122622,2016/0122623, 2016/0122624, and 2016/0122626, each of which isincorporated herein by reference in its entirety. Other suitable LPcompositions include compositions described, for example, in U.S. PatentApplication Publication No. 2017/0158947 to Kim et al., U.S. PatentApplication Publication No. 2017/0158948 to Kim et al., U.S. PatentApplication Publication No. 2018/0155505 to Kim et al., U.S. PatentApplication Publication No. 2019/0002754 to Yang et al., WO 2017/100327to Jackson et al., WO 2017/100331 to Jackson et al., and WO 2017/100329to Jackson et al., as well as SPE 179657 entitled “PermeabilityReduction Due to use of Liquid Polymers and Development of RemediationOptions” by Dwarakanath et al. (SPE IOR symposium at Tulsa 2016), eachof which is incorporated herein by reference in its entirety.

In some of these embodiments, the powder polymer for use in thesuspension is selected or tailored according to the characteristics ofthe reservoir for EOR treatment such as permeability, temperature andsalinity. Examples of suitable powder polymers include biopolymers suchas polysaccharides. For example, polysaccharides can be xanthan gum,scleroglucan, guar gum, a mixture thereof (e.g., any modificationsthereof such as a modified chain), etc. Indeed, the terminology“mixtures thereof” or “combinations thereof” can include “modificationsthereof” herein. Examples of suitable powder synthetic polymers includepolyacrylamides. Examples of suitable powder polymers include syntheticpolymers such as partially hydrolyzed polyacrylamides (HPAMs or PHPAs)and hydrophobically-modified associative polymers (APs). Also includedare co-polymers of polyacrylamide (PAM) and one or both of 2-acrylamido2-methylpropane sulfonic acid (and/or sodium salt) commonly referred toas AMPS (also more generally known as acrylamido tertiobutyl sulfonicacid or ATBS), N-vinyl pyrrolidone (NVP), and the NVP-based syntheticmay be single-, co-, or ter-polymers. In one embodiment, the powdersynthetic polymer is polyacrylic acid (PAA). In one embodiment, thepowder synthetic polymer is polyvinyl alcohol (PVA). Copolymers may bemade of any, combination or mixture above, for example, a combination ofNVP and ATBS.

In some embodiments, the carrier can comprise a mixture of surfactants(e.g., a surfactant and one or more co-surfactants, such as a mixture ofnon-ionic and anionic surfactants). Examples suitable surfactantsinclude ethoxylated surfactants, nonylphenol ethoxylates, alcoholethoxylates, internal olefin sulfonates, isomerized olefin sulfonates,alkyl aryl sulfonates, medium alcohol (C10 to C17) alkoxy sulfates,alcohol ether [alkoxy]carboxylates, alcohol ether [alkoxy]sulfates,alkyl sulfonate, α-olefin sulfonates (AOS), dihexyl sulfosuccinates,alkylpolyalkoxy sulfates, sulfonated amphoteric surfactants, andmixtures thereof.

In some embodiments, the carrier can further comprise a co-solvent(e.g., an alcohol, a glycol ether, or a combination thereof). In somecases, the co-solvent can comprise an alcohol ethoxylate (-EO—); analcohol alkoxylate (—PO-EO—); an alkyl polyglycol ether; an alkylphenoxy ethoxylate; an ethylene glycol butyl ether (EGBE); a diethyleneglycol butyl ether (DGBE); a triethylene glycol butyl ether (TGBE); apolyoxyethylene nonylphenylether, or a mixture thereof. In some cases,the co-solvent can comprise an alcohol selected from the group ofisopropyl alcohol (IPA), isobutyl alcohol (IBA) and secondary butylalcohol (SBA).

In some embodiments, the carrier can comprise an ionic surfactant,non-ionic surfactant, anionic surfactant, cationic surfactant,amphoteric surfactant, ketones, esters, ethers, glycol ethers, glycolether esters, lactams, cyclic ureas, alcohols, aromatic hydrocarbons,aliphatic hydrocarbons, alicyclic hydrocarbons, nitroalkanes,unsaturated hydrocarbons, halocarbons, alkyl aryl sulfonates (AAS),a-olefin sulfonates (AOS), internal olefin sulfonates (IOS), alcoholether sulfates derived from propoxylated Ci₂-C₂₀ alcohols, ethoxylatedalcohols, mixtures of an alcohol and an ethoxylated alcohol, mixtures ofanionic and cationic surfactants, disulfonated surfactants, aromaticether polysulfonates, isomerized olefin sulfonates, alkyl arylsulfonates, medium alcohol (C10 to C17) alkoxy sulfates, alcohol ether[alkoxy]carboxylates, alcohol ether [alkoxy]sulfates, primary amines,secondary amines, tertiary amines, quaternary ammonium cations, cationicsurfactants that are linked to a terminal sulfonate or carboxylategroup, alkyl aryl alkoxy alcohols, alkyl alkoxy alcohols, alkylalkoxylated esters, alkyl polyglycosides, alkoxy ethoxyethanolcompounds, isobutoxy ethoxyethanol (“iBDGE”), n-pentoxy ethoxyethanol(“n-PDGE”), 2-methylbutoxy ethoxyethanol (“2-MBDGE”), methylbutoxyethoxyethanol (“3-MBDGE”), (3,3-dimethylbutoxy ethoxyethanol(“3,3-DMBDGE”), cyclohexylmethyleneoxy ethoxyethanol (hereafter“CHMDGE”), 4-Methylpent-2-oxy ethoxyethanol (“MIBCDGE”), n-hexoxyethoxyethanol (hereafter “n-RIDGE”), 4-methylpentoxy ethoxyethanol(“4-MPDGE”), hutoxy ethanol, propoxy ethanol, hexoxy ethanol,isoproproxy 2-propanol, butoxy 2-propanol, propoxy 2-propanol, tertiarybutoxy 2-propanol, ethoxy ethanol, butoxy ethoxy ethanol, propoxy ethoxyethanol, hexoxy ethoxy ethanol, methoxy ethanol, methoxy 2-propanol andethoxy ethanol, n-methyl-2-pyrrolidone, dimethyl ethylene urea, andmixtures thereof.

“Substantially anhydrous” as used herein refers to a polymer suspensionwhich contains only a trace amount of water. Trace amount means nodetectable amount of water in one embodiment; less than or equal to 3wt. % water in another embodiment; and containing less than or equal toany of 2.5%, 2%, 1%, 0.9%, 0.8%, 0.7%, 0.6%, 0.5%, 0.4%, 0.3%, 0.2%,0.1%, 0.05% or 0.01% water in various embodiments. A reference to“polymer suspension” refers to a substantially anhydrous polymersuspension.

In other examples, LP compositions can comprise one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) dispersed oremulsified in one or more hydrophobic liquids. In some embodiments, theLP compositions can further comprise one or more emulsifying surfactantsand one or more inverting surfactants. In some embodiments, the LPcompositions can further comprise a small amount of water. For example,the LP compositions can further comprise less than 10% by weight (e.g.,less than 5% by weight, less than 4% by weight, less than 3% by weight,less than 2.5% by weight, less than 2% by weight, or less than 1% byweight) water, based on the total weight of all the components of the LPcomposition. In certain embodiments, the LP compositions can bewater-free or substantially water-free (i.e., the composition caninclude less than 0.5% by weight water, based on the total weight of thecomposition). The LP compositions can optionally include one or moreadditional components which do not substantially diminish the desiredperformance or activity of the composition. It will be understood by aperson having ordinary skill in the art how to appropriately formulatethe LP composition to provide necessary or desired features orproperties.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of one or more synthetic co-polymers (e.g.,acrylamide-(co)polymers); one or more emulsifier surfactants; and one ormore inverting surfactants.

In some embodiments, the LP composition can comprise one or morehydrophobic liquids having a boiling point at least 100° C.; at least39% by weight of particles of one or more acrylamide-(co)polymers; oneor more emulsifier surfactants; and one or more inverting surfactants.In certain embodiments, when the composition is fully inverted in anaqueous fluid, the composition affords an aqueous polymer solutionhaving a filter ratio (FR) (1.2 micron filter) of 1.5 or less. Incertain embodiments, the aqueous polymer solution can comprise from 500to 5000 ppm (e.g., from 500 to 3000 ppm) active polymer, and have aviscosity of at least 20 cP at 30° C.

In some embodiments, the LP compositions can comprise less than 10% byweight (e.g., less than 7% by weight, less than 5% by weight, less than4% by weight, less than 3% by weight, less than 2.5% by weight, lessthan 2% by weight, or less than 1% by weight) water prior to combinationwith the aqueous fluid, based on the total weight of all the componentsof the LP composition. In certain embodiments, the LP composition, priorto combination with the aqueous fluid, comprises from 1% to 10% water byweight, or from 1% to 5% water by weight, based on the total amount ofall components of the composition.

In some embodiments, the solution viscosity (SV) of a 0.1% solution ofthe LP composition can be greater than 3.0 cP, or greater than 5 cP, orgreater than 7 cP. The SV of the LP composition can be selected based,at least in part, on the intended actives concentration of the aqueouspolymer solution, to provide desired performance characteristics in theaqueous polymer solution. For example, in certain embodiments, where theaqueous polymer solution is intended to have an wives concentration ofabout 2000 ppm, it is desirable that the SV of a 0.1% solution of the LPcomposition is in the range of from 7.0 to 8.6, because at this level,the aqueous polymer solution has desired FR1.2 and viscosity properties.A liquid polymer composition with a lower or higher SV range may stillprovide desirable results, but may require changing the activesconcentration of the aqueous polymer solution to achieve desired FR1.2and viscosity properties. For example, if the liquid polymer compositionhas a lower SV range, it may be desirable to increase the activesconcentration of the aqueous polymer solution.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 39% polymer by weight (e.g., atleast 40% by weight, at least 45% by weight, at least 50% by weight, atleast 55% by weight, at least 60% by weight, at least 65% by weight, atleast 70% by weight, or at least 75% by weight), based on the totalamount of all components of the composition. In some embodiments, the LPcomposition can comprise 80% by weight or less polymer (e.g., 75% byweight or less, 70% by weight or less, 65% by weight or less, 60% byweight or less, 55% by weight or less, 50% by weight or less, 45% byweight or less, or 40% by weight or less), based on the total amount ofall components of the composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 39% to 80% by weight polymer (e.g.,from 39% to 60% by weight polymer, or from 39% to 50% by weightpolymer), based on the total weight of the composition.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theLP composition can comprise at least 10% polymer by weight (e.g., atleast 15% by weight, at least 20% by weight, at least 25% by weight, orat least 30% by weight), based on the total amount of all components ofthe composition. In some embodiments, the LP composition can compriseless than 38% by weight polymer (e.g., less than 35% by weight, lessthan 30% by weight, less than 25% by weight, less than 20% by weight, orless than 15% by weight), based on the total amount of all components ofthe composition.

The these embodiments, the LP composition can comprise an amount ofpolymer ranging from any of the minimum values described above to any ofthe maximum values described above. For example, in some embodiments,the LP composition can comprise from 10% to 38% by weight polymer (e.g.,from 10% to 35% by weight polymer, from 15% to 30% by weight polymer,from 15% to 35% by weight polymer, from 15% to 38% by weight polymer,from 20% to 30% by weight polymer, from 20% to 35% by weight polymer, orfrom 20% to 38% by weight polymer), based on the total weight of thecomposition.

Hydrophobic Liquid

In some embodiments, the LP composition can include one or morehydrophobic liquids. In some cases, the one or more hydrophobic liquidscan be organic hydrophobic liquids. In some embodiments, the one or morehydrophobic liquids each have a boiling point at least 100° C. (e.g., atleast 135° C., or at least 180° C.). If the organic liquid has a boilingrange, the term “boiling point” refers to the lower limit of the boilingrange.

In some embodiments, the one or more hydrophobic liquids can bealiphatic hydrocarbons, aromatic hydrocarbons, or mixtures thereof.Examples of hydrophobic liquids include but are not limited towater-immiscible solvents, such as paraffin hydrocarbons, naphthenehydrocarbons, aromatic hydrocarbons, olefins, oils, stabilizingsurfactants, and mixtures thereof. The paraffin hydrocarbons can besaturated, linear, or branched paraffin hydrocarbons. Examples ofsuitable aromatic hydrocarbons include, but are not limited to, tolueneand xylene. In certain embodiments; the hydrophobic liquid can comprisean oil, for example, a vegetable oil, such as soybean oil, rapeseed oil,canola oil, or a combination thereof, and any other oil produced fromthe seed of any of several varieties of the rape plant.

In some embodiments, the amount of the one or more hydrophobic liquidsin the inverse emulsion or LP composition is from 20% to 60%, from 25%to 54%, or from 35% to 54% by weight, based on the total amount of allcomponents of the LP composition.

Synthetic (Co)Polymers

In some embodiments, the LP composition includes one or more synthetic(co)polymers, such as one or more acrylamide containing (co)polymers. Asused herein, the terms “polymer,” “polymers,” “polymeric,” and similarterms are used in their ordinary sense as understood by one skilled inthe art, and thus may be used herein to refer to or describe a largemolecule (or group of such molecules) that contains recurring units.Polymers may be formed in various ways, including by polymerizingmonomers and/or by chemically modifying one or more recurring units of aprecursor polymer, A polymer may be a “homopolymer” comprisingsubstantially identical recurring units formed by, e.g., polymerizing aparticular monomer. A polymer may also be a “copolymer” comprising twoor more different recurring units formed by, e.g., copolymerizing two ormore different monomers, and/or by chemically modifying one or morerecurring units of a precursor polymer. The term “terpolymer” may beused herein to refer to polymers containing three or more differentrecurring units. The term “polymer” as used herein is intended toinclude both the acid form of the polymer as well as its various salts.

In some embodiments, the one or more synthetic (co)polymers can be apolymer useful for enhanced oil recovery applications. The term“enhanced oil recovery” or “EOR” (also known as tertiary oil recovery),refers to a process for hydrocarbon production in which an aqueousinjection fluid comprising at least a water soluble polymer is injectedinto a hydrocarbon bearing formation.

In some embodiments, the one or more synthetic (co)polymers comprisewater-soluble synthetic (co)polymers. Examples of suitable synthetic(co)polymers include acrylic polymers, such as polyacrylic acids,polyacrylic acid esters, partly hydrolyzed acrylic esters, substitutedpolyacrylic acids such as polymethacrylic acid and polymethacrylic acidesters, polyacrylamides, partly hydrolyzed polyacrylamides, andpolyacrylamide derivatives such as acrylamide tertiary butyl sulfonicacid (ATBS); copolymers of unsaturated carboxylic acids, such as acrylicacid or methacrylic acid, with olefins such as ethylene; propylene andbutylene and their oxides; polymers of unsaturated dibasic acids andanhydrides such as maleic anhydride; vinyl polymers, such as polyvinylalcohol (PVA), N-vinylpyrrolidone, and polystyrene sulfonate; andcopolymers thereof, such as copolymers of these polymers with monomerssuch as ethylene, propylene, styrene, methylstyrene, and alkyleneoxides. In some embodiments, the one or more synthetic (co)polymer cancomprise polyacrylic acid (PAA), polyacrylamide (PAM), acrylamidetertiary butyl sulfonic acid (ATBS) (or AMPS,2-acrylamido-2-methylpropane sulfonic acid), N-vinylpyrrolidone (NVP),polyvinyl alcohol (PVA), or a blend or copolymer of any of thesepolymers. Copolymers may be made of any combination above, for example,a combination of NVP and ATBS. In certain examples, the one or moresynthetic (co)polymers can comprise acrylamide tertiary butyl sulfonicacid (ATBS) (or AMPS, 2-acrylamido-2-methylpropane sulfonic acid) or acopolymer thereof.

In some embodiments, the one or more synthetic (co)polymers can compriseacrylamide (co)polymers. In some embodiments, the one or more acrylamide(co)polymers comprise water-soluble acrylamide (co)polymers. In variousembodiments, the acrylamide (co)polymers comprise at least 30% byweight, or at least 50% by weight actylamide units with respect to thetotal amount of all monomeric units in the (co)polymer.

Optionally, the acrylamide-(co)polymers can comprise, besidesacrylamide, at least one additional co-monomer. In example embodiments,the acrylamide-(co)polymer may comprise less than about 50%, or lessthan about 40%, or less than about 30%, or less than about 20% by weightof the at least one additional co-monomer. In some embodiments, theadditional comonomer can be a water-soluble, ethylenically unsaturated,in particular monoethylenically unsaturated, comonomer. Suitableadditional water-soluble comonomers include comonomers that are misciblewith water in any ratio, but it is sufficient that the monomers dissolvesufficiently in an aqueous phase to copolymerize with acrylamide. Insome cases, the solubility of such additional monomers in water at roomtemperature can be at least 50 g/L (e.g., at least 150 g/L, or at least250 g/L).

Other suitable water-soluble comonomers can comprise one or morehydrophilic groups. The hydrophilic groups can be, for example,functional groups that comprise one or more atoms selected from thegroup of O-, N-, S-, and P-atoms. Examples of such functional groupsinclude carbonyl groups >C—O, ether groups —O—, in particularpolyethylene oxide groups —(CH₂—CH₂—O—)_(n)—, where n is optionally anumber from 1 to 200, hydroxy groups —OH, ester groups —C(O)O—, primary,secondary or tertiary amino groups, ammonium groups, amide groups—C(O)—NH— or acid groups such as carboxyl groups —COOH, sulfonic acidgroups —SO₃H, phosphonic acid groups —PO₃H₂ or phosphoric acid groups—OP(OH)₃.

Examples of monoethylenically unsaturated comonomers comprising acidgroups include monomers comprising —COOH groups, such as acrylic acid ormethacrylic acid, crotonic acid, itaconic acid, maleic acid or fumaricacid, monomers comprising sulfonic acid groups, such as vinylsulfonicacid, allylsulfonic acid, 2-acrylamido-2-methylpropanesulfonic acid,2-methacrylamido-2-methylpropanesulfonic acid,2-acrylamidobutanesulfonic acid, 3-acrylamido-3-methylbutanesulfonicacid or 2-acrylamido-2,4,4-trimethylpentanesulfonic acid, or monomerscomprising phosphonic acid groups, such as vinylphosphonic acid,allylphosphonic acid, N-(meth)acrylamidoalkylphosphonic acids or(meth)acryloyloxyalkyl-phosphonic acids. Of course the monomers may beused as salts.

The —COOH groups in polyacrylamide-copolymers may not only be obtainedby copolymerizing acrylic amide and monomers comprising —COOH groups butalso by hydrolyzing derivatives of —COOH groups after polymerization.For example, the amide groups —CO—NH₂ of acrylamide may hydrolyze thusyielding —COOH groups.

Also to be mentioned are derivatives of acrylamide thereof, such as, forexample, N-methyl(meth)acrylamide, N,N′-dimethyl(meth)acrylamide, andN-methylolacrylamide, N-vinyl derivatives such as N-vinylformamide,N-vinylacetamide, N-vinylpyrrolidone or N-vinylcaprolactam, and vinylesters, such as vinyl formate or vinyl acetate. N-vinyl derivatives canbe hydrolyzed after polymerization to vinylamine units, vinyl esters tovinyl alcohol units.

Other example comonomers include monomers comprising hydroxy and/orether groups, such as, for example, hydroxyethyl(meth)acrylate,hydroxypropyl(meth)acrylate, allyl alcohol, hydroxyvinyl ethyl ether,hydroxyl vinyl propyl ether, hydroxyvinyl butyl ether orpolyethyleneoxide(meth)acrylates.

Other example comonomers are monomers having ammonium groups, i.emonomers having cationic groups. Examples comprise salts of3-trimethylammonium propylacrylamides or 2-trimethylammoniumethyl(meth)acrylates, for example the corresponding chlorides, such as3-trimethylammonium propylacrylamide chloride (DIMAPAQUAT) and2-trimethylammonium ethyl methacrylate chloride (MADAME-QUAT).

Other example monoethylenically unsaturated monomers include monomerswhich may cause hydrophobic association of the (co)polymers. Suchmonomers comprise besides the ethylenic group and a hydrophilic partalso a hydrophobic part. Such monomers are disclosed for instance in WO2012/069477, which is incorporated herein by reference in its entirety.

Other example comonomers include N-alkyl acrylamides and N-alkylquarternary acrylamides, where the alkyl group comprises, for example, aC2-C28 alkyl group.

In certain embodiments, each of the one or more acrylamide-(co)polymerscan optionally comprise crosslinking monomers, i.e. monomers comprisingmore than one polymerizable group. In certain embodiments, the one ormore acrylamide-(co)polymers may optionally comprise crosslinkingmonomers in an amount of less than 0.5%, or 0.1%, by weight, based onthe amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprises at least one monoethylenically unsaturated comonomercomprising acid groups, for example monomers which comprise at least onegroup selected from —COOH, —SO₃H or —PO₃H₂. Examples of such monomersinclude but are not limited to acrylic acid, methacrylic acid,vinylsulfonic acid, allylsulfonic acid or2-arcylamido-2-methylpropanesulfonic acid, particularly acrylic acidand/or 2-acrylamido-2-methylpropanesulfonic acid such as acrylic acid orthe salts thereof. The amount of such comonomers comprising acid groupscan be from 0.1% to 70%, from 1% to 50%, or from 10% to 50% by weightbased on the amount of all monomers.

In an embodiment, each of the one or more acrylamide-(co)polymerscomprise from 50% to 90% by weight of acrylamide units and from 10% to50% by weight of acrylic acid units and/or their respective salts, basedon the total weight of all the monomers making up the copolymer. In anembodiment, each of the one or more acrylamide-(co)polymers comprisesfrom 60% to 80% by weight of acrylamide units and from 20% to 40% byweight of acrylic acid units, based on the total weight of all themonomers making up the copolymer.

In some embodiments, the one or more synthetic (co)polymers (e.g., theone or more acrylamide (co)polymers) are in the form of particles, whichare dispersed in the emulsion or LP. In some embodiments, the particlesof the one or more synthetic (co)polymers can have an average particlesize of from 0.4 μm to 5 μm, or from 0.5 μm to 2 μm. Average particlesize refers to the d₅₀ value of the particle size distribution (numberaverage) as measured by laser diffraction analysis.

In some embodiments, the one or more synthetic (co)polymers the one ormore acrylamide (co)polymers) can have a weight average molecular weight(M_(w)) of from 5,000,000 g/mol to 30,000,000 g/mol; from 10,000,000g/mol to 25,000,000 g/mol; or from 15,000,000 g/mol to 25,000,000 g/mol.

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)dispersed in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be at least 39% byweight, based on the total weight of the composition. In some of theseembodiments, the amount of the one or more synthetic (co)polymers (e.g.,one or more arcylamide-(co)polymers) in the LP composition can be from39% to 80% by weight, or from 40% to 60% by weight, or from 45% to 55%by weight, based on the total amount of all components of thecomposition (before dilution), In some embodiments, the amount of theone or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition is 39%, 40%, 41%, 42%,43%, 44%. 45%, 46%, 47%, 48%, 49%, 50?, 51%. 57%, 53%, 54%, 55%, 56%,57%, 58%, 59%, 60%, or higher, by weight, based on the total amount ofall components of the composition (before dilution).

In some embodiments, the LP composition can comprise one or moresynthetic (co)polymers (e.g., one or more acrylamide (co)polymers)emulsified in one or more hydrophobic liquids. In these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide (co)polymers) in the LP composition can be less than 38% byweight, less than 35% by weight, or less than 30% by weight based on thetotal weight of the composition. In some of these embodiments, theamount of the one or more synthetic (co)polymers (e.g., one or moreacrylamide-(co)polymers) in the LP composition can be from 10% to 35% byweight, from 10% to 38% by weight, from 15% to 30% by weight, from 15%to 38% by weight, from 20% to 38% by weight, or from 20% to 30% byweight, based on the total amount of all components of the composition(before dilution), In some embodiments, the amount of the one or moresynthetic (co)polymers (e.g., one or more acrylamide-(co)polymers) inthe LP composition is 38%, 37%, 36%, 35%, 34%. 33%, 32%, 31%, 30%, 29%,78%, 27%, 26%, 25%, 24%, 23%, 22%, 71%, 20%, 19%, 18%, 17%, 16%, 15%,14%, 13%, 12%, 11%, or less, by weight, based on the total amount of allcomponents of the composition (before dilution).

Emulsifying Surfactants

In some embodiments, the LP composition can include one or moreemulsifying surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants capable of stabilizingwater-in-oil-emulsions. Emulsifying surfactants, among other things, inthe emulsion, lower the interfacial tension between the water and thewater-immiscible liquid so as to facilitate the formation of awater-in-oil polymer emulsion. It is known in the art to describe thecapability of surfactants to stabilize water-in-oil-emulsions oroil-in-water emulsions by using the so called “HLB-value”(hydrophilic-lipophilic balance), The HLB-value usually is a number from0 to 20. In surfactants having a low HLB-value the lipophilic parts ofthe molecule predominate and consequently they are usually goodwater-in-oil emulsifiers. In surfactants having a high HLB-value thehydrophilic parts of the molecule predominate and consequently they areusually good oil-in-water emulsifiers. In some embodiments, the one ormore emulsifying surfactants are surfactants having an HLB-value of from2 to 10, or a mixture of surfactant having air HLB-value of from 2 to10.

Examples of suitable emulsifying surfactants include, but are notlimited to, sorbitan esters, in particular sorbitan monoesters withC12-C18-groups such as sorbitan monolaurate (HLB approx. 8.5), sorbitanmonopalmitate (HLB approx. 7.5), sorbitan monostearate (HLB approx.4.5), sorbitan monooleate (HLB approx. 4); sorbitan esters with morethan one ester group such as sorbitan tristearate (HLB approx. 2),sorbitan trioleate (HLB approx. 2); ethoxylated fatty alcohols with 1 to4 ethyleneoxy groups, e.g. polyoxyethylene (4) dodecylether ether (HLBvalue approx. 9), polyoxyethylene (2) hexadecyl ether (HLB value approx.5), and polyoxyethylene (2) oleyl ether (HLB value approx. 4).

Exemplary emulsifying surfactants include, but are not limited to,emulsifiers having HLB values of from 2 to 10 (e.g., less than 7).Suitable such emulsifiers include the sorbitan esters, phthalic esters,fatty acid glycerides, glycerine esters, as well as the ethoxylatedversions of the above and any other well known relatively low HLBemulsifier, Examples of such compounds include sorbitan monooleate, thereaction product of oleic acid with isopropanolamide, hexadecyl sodiumphthalate, decyl sodium phthalate, sorbitan stearate, ricinoleic acid,hydrogenated ricinoleic acid, glyceride monoester of lauric acid,glyceride monoester of stearic acid, glycerol diester of oleic acid,glycerol triester of 12-hydroxystearic acid, glycerol triester ofricinoleic acid, and the ethoxylated versions thereof containing 1 to 10moles of ethylene oxide per mole of the basic emulsifier. Thus, anyemulsifier can be utilized which will permit the formation of theinitial emulsion and stabilize the emulsion during the polymerizationreaction. Examples of emulsifying surfactants also include modifiedpolyester surfactants, anhydride substituted ethylene copolymers,N,N-dialkanol substituted fatty amides, and tallow amine ethoxylates.

In an embodiment, the inverse emulsion or LP composition comprises from0% to 5% by weight (e.g., from 0.05% to 5%, from 0.1% to 5%, or from0.5% to 3% by weight) of the one or more emulsifying surfactants, basedon the total weight of the composition. These emulsifying surfactantscan be used alone or in mixtures. In some embodiments, the inverseemulsion or LP composition can comprise less than 5% by weight (e.g.,less than 4% by weight, or less than 3% by weight) of the one or moreemulsifying surfactants, based on the total weight of the composition.

Process Stabilizing Agents

In some embodiments, the LP composition can optionally include one ormore process stabilizing agents. The process stabilizing agents aim atstabilizing the dispersion of the particles ofpolyacrylamide-(co)polymers in the organic, hydrophobic phase andoptionally also at stabilizing the droplets of the aqueous monomer phasein the organic hydrophobic liquid before and in course of thepolymerization or processing of the LP composition. The term“stabilizing” means in the usual manner that the agents prevent thedispersion from aggregation and flocculation.

The process stabilizing agents can be any stabilizing; agents, includingsurfactants, which aim at such stabilization. In certain embodiments,the process stabilizing agents can be oligomeric or polymericsurfactants. Due to the fact that oligomeric and polymeric surfactantscan have many anchor groups they absorb very strongly on the surface ofthe particles and furthermore oligomers/polymers are capable of forminga dense steric barrier on the surface of the particles which preventsaggregation. The number average molecular weight Mn of such oligomericor polymeric surfactants may for example range from 500 to 60,000 g/mol(e.g., from 500 to 10,000 g/mol, or from 1,000 to 5,000 g/mol). Suitableoligomeric and/or polymeric surfactants for stabilizing polymerdispersions are known to the skilled artisan. Examples of suchstabilizing polymers comprise amphiphilic block copolymers, comprisinghydrophilic and hydrophobic blocks, amphiphilic copolymers comprisinghydrophobic and hydrophilic monomers and amphiphilic comb polymerscomprising a hydrophobic main chain and hydrophilic side chains oralternatively a hydrophilic main chain and hydrophobic side chains.

Examples of amphiphilic block copolymers comprise block copolymerscomprising a hydrophobic block comprising alkylarcylates having longeralkyl chains, e.g., C6 to C22-alkyl chains, such as for instancehexyl(meth)acrylate, 2-ethylhexyl(meth)actylate, octyl(meth)acrylate,do-decyl(meth)acrylate, hexadecyhmeth)acrylate oroctadecyl(meth)acrylate. The hydrophilic block may comprise hydrophilicmonomers such as acrylic acid, methacrylic acid or vinyl pyrrolidone.

Inverting Surfactants

In some embodiments, the LP composition optionally can include one ormore inverting surfactants. In some embodiments, the one or moreemulsifying surfactants are surfactants which can be used to acceleratethe formation of an aqueous polymer solution (e.g., an inverted(co)polymer solution) after mixing the inverse emulsion or LPcomposition with an aqueous fluid.

Suitable inverting surfactants are known in the art, and include, forexample, nonionic surfactants comprising a hydrocarbon group and apolyalkylenoxy group of sufficient hydrophilic nature. In some cases,nonionic surfactants defined by the general formula R¹—O—(CH(R²)CH₂—O)_(n)H (I) can be used, wherein R¹ is a C₈-C₂₂-hydrocarbon group,such as an aliphatic C₁₀-C₁₈-hydrocarbon group, n is a number of ≥4,optionally ≥6, and R² is methyl or ethyl, with the proviso that at least50% of the groups R² are H. Examples of such surfactants includepolyethoxylates based on C₁₀-C₁₈-alcohols such as C_(12/14)-, C_(14/18)-or C_(16/18)-fatty alcohols, C₁₃- or C_(13/15)-oxoalcohols. TheHLB-value can be adjusted by selecting the number of ethoxy groups.Specific examples include tridecylalcohol ethoxylates comprising from 4to 14 ethylenoxy groups (e.g., tridecyalcohol-8 EO (HLB-value approx.13-14)) or C_(12/14) fatty alcohol ethoxylates (e.g., C_(12/14).8 EO(HLB-value approx. 13)). Examples of emulsifying surfactants alsoinclude modified polyester surfactants, anhydride substituted ethylenecopolymers, N,N-dialkanol substituted fatty amides, and tallow amineethoxylates.

Other suitable inverting surfactants include anionic surfactants, suchas, for example, surfactants comprising phosphate or phosphoric acidgroups.

In some embodiments, the one or more inverting surfactants can comprisepolyoxyethylene sorbitol tetraoleate, C₁₂₋₁₄ branched ethoxylatedalcohol, polyethylene glycol monoleate. In certain embodiments, the oneor more inverting surfactants can comprise from 1 to 20 mole %polyoxyethylene sorbitol tetraoleate, from 60 to 80 mole % C₁₂₋₁₄branched ethoxylated alcohol and about 15 to about 25 mole %polyethylene glycol monoleate.

In some embodiments, the amount of the one or more inverting surfactantsin the inverse emulsion or LP composition is from 1% to 10% (e.g., from1% to 5%) by weight. based on the total amount of all components of theinverse emulsion or LP composition.

In certain embodiments, the one or more inverting surfactants can beadded to the inverse emulsion or LP composition directly afterpreparation of the composition comprising the one or more acrylamide(co)polymers dispersed in one or more hydrophobic liquids, andoptionally the one or more emulsifying surfactants (i.e., the inverseemulsion or liquid dispersion polymer composition which is transportedfrom the location of manufacture to the location of use alreadycomprises the one or more inverting surfactants). In another embodimentthe one or more inverting surfactants may be added to the inverseemulsion or LP composition at the location of use (e.g., at an off-shoreproduction site).

Stabilizing Agents

Inverse emulsion and liquid polymer compositions can form gels andexperience separation of their oil and water phases over time. Inparticular, the shelf-life stability of such compositions having highpolymer actives may decrease as the solids content is raised. In someinstances, such compositions may deteriorate to form an oil film and ahard cake in packaging within the amount of time it takes to manufactureand transport the compositions to the platform (e.g., about 30 days),The hard cake may not be readily redistributed in the composition, whichresults in lower overall polymer actives in the deterioratedcomposition. Thickening additives may be used to minimize settling ofthe inverse emulsion and liquid polymer compositions, however they mayhave a detrimental effect on the filter ratio of the compositions.

Accordingly, the LP compositions can optionally comprise one or morestabilizing agents (e.g., one or more siloxane polyether compounds, oneor more poly(alkyl)acrylate compounds, or a combination thereof) whichmay prevent or minimize sedimentation and/or caking of solids in theliquid polymer or inverse emulsion compositions. In embodiments, thecompositions according to the embodiments comprise an acrylamide(co)polymer and one or more stabilizing agents chosen from one or moresiloxane polyether compounds, one or more poly(alkyl)acrylate compounds,or a combination thereof, Such additives are described, for example, inU.S. Patent Application Publication No. 2019/0002754 to Yang et al.,which is incorporated herein by reference in its entirety.

The term “stabilizing” means, as in the usual manner, that thestabilizing agents prevent the dispersion from aggregation andflocculation, or prevent sedimentation and/or caking of the solids orparticles in the composition and/or creation of separated oil phase. Asused herein, “caking” refers to the formation of lumps or masses fromthe solids or particles in the composition. Generally, hard caking ischaracterized by strong, adhesive forces between the particles, and/orthe formation of a cake which is difficult to redisperse. Soft cakingmay be characterized by weak, adhesive forces between the particles,and/or the formation of a cake which is more readily redispersed.Ideally, the solids and particles of the composition remainsubstantially evenly dispersed in the liquids of the composition. Incertain embodiments, the stabilizing agent increases the stability ofthe LP composition such that the composition shows no caking, or onlysoft caking, after about 20, about 30, about 40, about 50, about 60,about 70, about 80, about 90 or about 100 days at a temperature in therange of about 30 to 50° C. In certain embodiments, compositions whichundergo soft caking are re-dispersable with gentle agitation orstirring. In certain embodiments, the compositions show no caking, oronly soft caking, after about 20, about 30, about 40, about 50, about60, about 70, about 80, about 90 or about 100 days at a temperature inthe range of about 30 to 50° C. In embodiments, less than about 10%,about 5%, or about 2% of the solids or particles in the composition havesettled into a soft cake after about 20, about 30, about 40, about 50,about 60, about 70, about 80, about 90 or about 100 days at atemperature in the range of about 30 to 50° C.

The one or more stabilizing agents can be chosen from one or moresiloxane polyether compounds, one or more poly(alkyl)acrylate compounds,or a combination thereof. In some embodiments, the LP composition cancomprise one or more siloxane polyether compounds. In some embodiments,the LP composition can comprise one or more poly(alkyl)acrylatecompounds. In some embodiments, the LP composition can comprise one ormore siloxane polyether compounds and one or more poly(alkyl)acrylatecompounds.

In an embodiment, the Lp composition comprises about 0.5% to about 8%,about 1% to about 5%, about 1.5% to about 5%, or about 1.5% to about3.5% by weight of the one or more stabilizing agents (e.g., one or moresiloxane polyether compounds, one or more poly(alkyl)acrylate compounds,or a combination thereof).

In embodiments, the one or more stabilizing agents can comprise one ormore siloxane polyether compounds, and the one or more siloxanepolyether compounds can be present in amounts of greater than about0.5%, greater than about 1%, or greater than about 2% by weight of thetotal liquid polymer or inverse emulsion composition.

In embodiments, the composition comprises a siloxane polyether compoundwith terminal or pendent ethoxylation. In an embodiment, the compositioncomprises a siloxane polyether compound with terminal ethoxylation. Inan embodiment, the composition comprises a siloxane polyether compoundof Formula I:

wherein

each R is independently selected from methyl, ethyl and propyl;

each A independently represents a chain of ethylene oxide (EO) and,optionally, propylene oxide (PO) units, which may be present in block,alternating or random arrangement, wherein the quantity of EO units isin the range of 4 to 30 and the quantity of PO units is in the range of0 to 30; and

k is an integer from 5 to 30.

In embodiments, the A units are the same. In embodiments, the A unitsare different. In embodiments, the A units comprise only EO units. Inembodiments, the A units comprises both EO and PO units, which arepresent in block arrangement, for example each A group consists of twoor more, or three or more, blocks of EO or PO units. In embodiments, theA units comprises both EO and PO units, which are present in randomarrangement. In embodiments, the A units comprises both EO and PO units,which are present in an alternating arrangement, e.g. an EO-PO-EO-POchain.

In embodiments, R is methyl. In embodiments, R is ethyl. In embodiments,R is propyl, for example n-propyl or isopropyl.

In an embodiment, the composition comprises a siloxane polyethercompound with pendant ethoxylation. In an embodiment, the compositioncomprises a siloxane polyether compound of Formula II:

wherein

each R is independently selected from methyl, ethyl and propyl;

each D independently represents a chain of ethylene oxide (EO) and,optionally, propylene oxide (PO) units, which may be present in block,alternating or random arrangement, wherein the quantity of EO units isin the range of 3 to 50 and the quantity of PO units is in the range of0 to 40;

R′ is hydroxyl or acetate;

y is an integer from 5 to 30; and

k is an integer from 5 to 100.

In certain embodiments, each D independently represents a chain ofethylene oxide (EO) and propylene oxide (PO) units, which may be presentin block, alternating or random arrangement, wherein the quantity of EOunits is in the range of 3 to 50 and the quantity of PO units is in therange of 3 to 40.

In embodiments, the D units are the same. In embodiments, the D unitsare different. In embodiments, the units comprise only EO units. Inembodiments, the D units comprises both EO and PO units, which arepresent in block arrangement, for example each D group consists of twoor more, or three or more, blocks of EO or PO units. In embodiments, theD units comprises both EO and PO units, which are present in randomarrangement. In embodiments, the D units comprises both EO and PO units,which are present in an alternating arrangement, e.g. an EO-PO-EO-POchain.

In embodiments, R is methyl. In embodiments, R is ethyl. In embodiments,R is propyl, for example n-propyl or isopropyl.

In embodiments, R′ is hydroxyl. In embodiments, R′ is acetate.

In embodiments, the siloxane polyether compound is, for example, asiloxane polyether with pendent ethoxylation and EO/PO ratio in therange of about 15/85 to about 85/15; about 15/85 to about 50/50; orabout 25/75 to about 40/60. In embodiments, the siloxane polyethercompound generally includes more EO and/or PO units than siloxane unitsby weight of the compound. In embodiments, the siloxane polyethercompound has pendent ethoxylation and the value of y is greater than thevalue of k. In embodiments, the siloxane polyether compound has pendentethoxylation and the k:y ratio is in the range of about 1:3 to about1:100.

In embodiments, the siloxane polyether compound is, for example, asiloxane polyether with pendent ethoxylation and an HLB value of about10 to about 14.

In embodiments, the siloxane polyether compound is selected from thefollowing commercially available products: SG3381 from Wacker, Tegopren5825 from Evonik, Tegopren 5863 from Evonik, and KF-355A from ShinEtsu.

In embodiments, the one or more stabilizing agents can comprise one ormore poly(alkyl)acrylate compounds, and the one or morepoly(alkyl)acrylate compounds can be present in amounts of about 0.5% toabout 1.5%, or about 0.5% to about 1.5%, by weight of the total LPcomposition.

In embodiments, the composition comprises a poly(alkyl)acrylate compoundof Formula III:

wherein

R′ is a straight or branched C6-14 alkyl group; and

p is an integer from 2000 to 5000.

In an embodiments, the poly(alkyl)acrylate compound is, for example,poly(2-ethylhexyl)acrylate.

In embodiments, the poly(2-ethylhexyl)acrylate has a MW in the rangeabout 90000 to 95000 Daltons.

In embodiments, the compositions may further comprise additionalstabilizing agents, for example agents which aim at such stabilizationof the dispersion or emulsion, such as oligomeric or polymericsurfactants. Due to the fact that oligomeric and polymeric surfactantshave many anchor groups they absorb very strongly on the surface of theparticles and furthermore oligomers/polymers are capable of forming adense steric barrier on the surface of the particles which preventsaggregation. The number average molecular weight Mn of such oligomericor polymeric surfactants may for example range from 500 to 60,000Daltons, from 500 to 10,000 Daltons, or from 1,000 to 5,000 Daltons.Oligomeric and/or polymeric surfactants for stabilizing polymerdispersions are known to the skilled artisan. Examples of suchstabilizing polymers comprise amphiphilic copolymers, comprisinghydrophilic and hydrophobic moiety, amphiphilic copolymers comprisinghydrophobic and hydrophilic monomers and amphiphilic comb polymerscomprising a hydrophobic main chain and hydrophilic side chains oralternatively a hydrophilic main chain and hydrophobic side chains.

Examples of amphiphilic copolymers comprise copolymers comprising ahydrophobic moiety comprising alkylacrylates having longer alkyl chains,e.g. C6 to C22-alkyl chains, such as for instance hexyl(meth)acrylate,2-ethylhexyl(meth)acrylate, octyl(meth)acrylate, do-decyl(meth)acrylate,hexadecyl(meth)acrylate or octadecyl(meth)acrylate. The hydrophilicmoiety may comprise hydrophilic monomers such as acrylic acid,methacrylic acid or vinyl pyrrolidone.

In an embodiment, the LP composition comprises about 0% to about 8%,about 0.1% to about 5%, or about 1% to about 5% by weight of the one ormore additional stabilizing agents described herein.

Other Components

Optional further components can be added to the inverse emulsion or LPcomposition. Examples of such components comprise radical scavengers,oxygen scavengers, chelating agents, biocides, stabilizers, orsacrificial agents.

Methods for Preparing Surfactant Compositions

Also provided are methods for preparing the concentrated liquidsurfactant compositions described herein. Methods for preparing theconcentrated liquid surfactant compositions can comprise combining an LPcomposition, a surfactant package, and a co-solvent to form thesurfactant composition. The surfactant package can comprise from 0.2% to98% by weight of the surfactant composition. The co-solvent can comprisefrom greater than 0% to 95% by weight of the surfactant composition. TheLP composition can comprise from 0.1% to 60% by weight of the surfactantcomposition. The surfactant composition can have a total water contentof from 0.5% to 20% by weight, based on the total weight of thesurfactant composition.

In some embodiments, combining the LP composition, the surfactantpackage, and the co-solvent can comprise mixing from 0.1 parts to 60parts of the LP composition with from 0.2 parts to 98 parts of thesurfactant composition and from greater than 0 parts to 95 parts of theco-solvent. In some embodiments, combining the LP composition, thesurfactant package, and the co-solvent can comprise adding the LPcomposition to a mixture comprising the surfactant package and theco-solvent.

Preparation Aqueous Surfactant-Polymer Solutions

Provided herein are aqueous surfactant-polymer solutions, as well asmethods of preparing the aqueous surfactant-polymer solutions fromsurfactant compositions, such as those described above, using a singlestage mixing process.

Methods for preparing an aqueous surfactant-polymer solution from thesurfactant compositions described herein can comprise combining thesurfactant composition with an aqueous fluid in a single stage mixingprocess to provide an aqueous surfactant-polymer solution having aconcentration of one or more (co)polymers (e.g., one or more synthetic(co)polymers, such as one or more acrylamide (co)polymers) of from 50 to15,000 ppm.

In some embodiments, the aqueous surfactant-polymer solution can have aconcentration of one or more (co)polymers (e.g., one or more synthetic(co)polymers, such as one or more acrylamide (co)polymers) of at least50 ppm (e.g., at least 100 ppm, at least 250 ppm, at least 500 ppm, atleast 750 ppm, at least 1000 ppm, at least 1500 ppm, at least 2000 ppm,at least 2500 ppm, at least 3000 ppm, at least 3500 ppm, at least 4000ppm, at least 4500 ppm, at least 5000 ppm, at least 5500 ppm, at least6000 ppm, at least 6500 ppm, at least 7000 ppm, at least 7500 ppm, atleast 8000 ppm, at least 8500 ppm, at least 9000 ppm, at least 9500 ppm,at least 10,000 ppm, at least 10,500 ppm, at least 11,000 ppm, at least11,500 ppm, at least 12,000 ppm, at least 12,500 ppm, at least 13,000ppm, at least 13,500 ppm, at least 14,000 ppm, or at least 14,500 ppm).

In some embodiments, the aqueous surfactant-polymer solution can have aconcentration of one or more (co)polymers (e.g., one or more synthetic(co)polymers, such as one or more acrylamide (co)polymers) of 15,000 ppmor less (e.g., 14,500 ppm or less, 14,000 ppm or less, 13,500 ppm orless, 13,000 ppm or less, 12,500 ppm or less, 12,000 ppm or less, 11,500ppm or less, 11,000 ppm or less, 10,500 ppm or less, 10,000 ppm or less,9,500 ppm or less, 9,000 ppm or less, 8,500 ppm or less, 8,000 ppm orless, 7,500 ppm or less, 7,000 ppm or less, 6,500 ppm or less, 6,000 ppmor less, 5,500 ppm or less, 5,000 ppm or less, 4500 ppm or less, 4000ppm or less, 3500 ppm or less, 3000 ppm or less, 2500 ppm or less, 2000ppm or less, 1500 ppm or less, 1000 ppm or less, 750 ppm or less, 500ppm or less, 250 ppm or less, or 100 ppm or less).

The aqueous surfactant-polymer solution can have a concentration of oneor more (co)polymers (e.g., one or more synthetic (co)polymers, such asone or more acrylamide (co)polymers) ranging from any of the minimumvalues described above to any of the maximum values described above. Forexample, in some embodiments, the aqueous surfactant-polymer solutioncan have a concentration of one or more (co)polymers (e.g., one or moresynthetic (co)polymers, such as one or more acrylamide (co)polymers) offrom 500 to 5000 ppm (e.g., from 500 to 3000 ppm, or from 500 to 1500ppm).

In some embodiments, the aqueous surfactant-polymer solution can be anaqueous unstable colloidal suspension. In other embodiments, the aqueoussurfactant-polymer solution can be an aqueous stable solution.

In some embodiments, the aqueous surfactant-polymer solution can have afilter ratio of 1.5 or less (e.g., 1.45 or less, 1.4 or less, 1.35 orless, 1.3 or less, 1.25 or less, 1.2 or less. 1.15 or less, 1.1 or less,or less than 1.05) at 15 psi using a 1.2 μm filter. In some embodiments,the aqueous surfactant-polymer solution can have a filter ratio ofgreater than 1 (e.g., at least 1.05, at least 1.1, at least 1.15, atleast 1.2, at least 1.25, at least 1.3, at least 1.35, at least 1.4, orat least 1.45) at 15 psi using a 1.2 μm filter.

The aqueous surfactant-polymer solution can a filter ratio at 15 psiusing a 1.2 μm filter ranging from any, of the minimum values describedabove to any of the maximum values described above. For example, in someembodiments, the aqueous surfactant-polymer solution can have a filterratio of from 1 to 1.5 (e.g., from 1.1 to 1.4, or from 1.1 to 1.3) at 15psi using a 1.2 μm filter.

In certain embodiments, the aqueous surfactant-polymer solution can havea viscosity based on shear rate, temperature, salinity, polymerconcentration, and polymer molecular weight. In some embodiments, theaqueous surfactant-polymer solution can have a viscosity of from 2 cP to100 cP, where the 2 cP to 100 cP is an output using the ranges in thefollowing table:

Polymer viscosity (cP)  2~100 Shear rate (1/sec)  0.1~1000  Temperature(° C.)  1~120 Salinity (ppm)     0~250,000 Polymer concentration (ppm)   50~15,000 Polymer molecular weight (Dalton)  2M~26M

In some embodiments, the aqueous surfactant-polymer solution can have aviscosity of from 25 cP to 35 cP at 30° C. In some embodiments, theaqueous surfactant-polymer solution can have a viscosity of greater than10 cP at 40° C. In certain embodiments, the aqueous surfactant-polymersolution can have a viscosity of from 20 cP to 30 cP at 40° C.

In some embodiments, when the surfactant composition is combined with anaqueous fluid, providing an aqueous surfactant-polymer solution havingfrom 50 to 15,000 ppm, from 500 to 5,000 ppm, or from 500 to 3000 ppm,active polymer, the aqueous surfactant-polymer solution has a viscosityof at least 20 cP at 40° C., and a filter ratio (FR) (1.2 micron filter)of 1.5 or less. In certain embodiments, when the surfactant compositionis combined with in an aqueous fluid, providing an aqueoussurfactant-polymer solution having from 50 to 15,000 ppm, from 500 to5000 ppm, or from 500 to 3000 ppm, active polymer, the aqueoussurfactant-polymer solution has a viscosity of at least 20 cP at 30° C.,and a filter ratio (FR) (1.2 micron filter) of 1.5 or less.

The ability of a surfactant-polymer solution to reduce the interfacialtension of a mixture of hydrocarbons and fluids may be evaluated usingknown techniques. For example, an interfacial tension value for amixture of hydrocarbons and water may be determined using a spinningdrop tensiometer. An amount of the surfactant-polymer solution may beadded to the hydrocarbon/water mixture and an interfacial tension valuefor the resulting fluid may be determined. A high interfacial tensionvalue (e.g., greater than about 10 dynes/cm) may indicate the inabilityof the hydrocarbons and water to form a fluid emulsion. As used herein,an “emulsion” refers to a dispersion of one immiscible fluid into asecond fluid by addition of a composition that reduces the interfacialtension between the fluids to achieve stability. The inability of thefluids to mix may be due to high surface interaction energy between thetwo fluids. Low interfacial tension values may indicate less surfaceinteraction between the two immiscible fluids. Less surface interactionenergy between two immiscible fluids may result in the mixing of the twofluids to form an emulsion. Fluids with low interfacial tension valuesmay be mobilized to a well bore due to reduced capillary forces andsubsequently produced from a hydrocarbon containing formation.

In some embodiments, the surfactant-polymer solution can exhibit a lowinterfacial tension (e.g., a surface tension of 0.01 dynes/cm or less).For example, in some embodiments, the surfactant-polymer solution canexhibit an interfacial tension that ranges from 0.00001 dynes/cm to 0.01dynes/cm (e.g., from 0.00005 dynes/cm to 0.01 dynes/cm, from 0.0001dynes/cm to 0.01 dynes/cm, from 0.0005 dynes/cm to 0.01 dynes/cm, from0.001 dynes/cm to 0.01 dynes/cm, or from 0.005 dynes/cm to 0.01dynes/cm).

In some cases, combining a surfactant composition with an aqueous fluidcan comprise inverting the surfactant composition in an aqueous fluid toprovide the aqueous surfactant-polymer solution. In these embodiments,the aqueous surfactant-polymer solution can be said to be an “invertedsurfactant-polymer solution.” As used herein, “inverted” refers to thepoint at which the viscosity of the aqueous surfactant-polymer solutionhas substantially reached a consistent viscosity. In practice, this maybe determined for example by measuring viscosity of the aqueoussurfactant-polymer solution periodically over time and when threeconsecutive measurements are within the standard of error for themeasurement, then the composition is considered inverted. In someembodiments, inversion of the surfactant composition forms an invertedsurfactant-polymer solution in 30 minutes or less (e.g., 15 minutes orless, 10 minutes or less, 5 minutes or less, or less).

As described above, methods for preparing an aqueous surfactant-polymersolution from a surfactant composition comprising one or more synthetic(co)polymers (e.g., one or more acrylamide (co)polymers) can comprisecombining the surfactant composition with an aqueous fluid in a singlestage mixing process to provide an aqueous surfactant-polymer solutionhaving a concentration of one or more synthetic (co)polymers (e.g., oneor more acrylamide (co)polymers) of from 50 to 15,000 ppm. The singlestage mixing process can comprise applying a specific mixing energy ofat least 0.10 kJ/kg to the surfactant composition and the aqueous fluid.

In some embodiments, the single stage mixing process can compriseapplying a specific mixing energy of at least 0.10 kJ/kg (e.g., at least0:15 kJ/kg, at least 0.20 kJ/kg, at least 0.25 kJ/kg, at least 0.30kJ/kg, at least 0.35 kJ/kg, at least 0.40 kJ/kg, at least 0.45 kJ/kg, atleast 0.50 kJ/kg, at least 0.55 kJ/kg, at least 0.60 kJ/kg, at least0.65 kJ/kg, at least 0.70 kJ/kg, at least 0.75 kJ/kg, at least 0.80kJ/kg, at least 0.85 kJ/kg, at least 0.90 kJ/kg, at least 0.95 kJ/kg, atleast 1.00 kJ/kg, at least 1.05 kJ/kg, at least 1.10 kJ/kg, at least1.15 kJ/kg, at least 1.20 kJ/kg, at least 1.25 kJ/kg, at least 1.30kJ/kg, at least 1.35 kJ/kg, at least 1.40 kJ/kg, or at least 1.45 kJ/kg)to the surfactant composition and the aqueous fluid. In someembodiments, the single stage mixing process can comprise applying aspecific mixing energy of 1.50 kJ/kg or less (e.g., 1.45 kJ/kg or less,1.40 kJ/kg or less, 1.35 kJ/kg or less, 1.30 kJ/kg or less, 1.25 kJ/kgor less, 1.20 kJ/kg or less, 1.15 kJ/kg or less, 1.10 kJ/kg or less,1.05 kJ/kg or less, 1.00 kJ/kg or less, 0.95 kJ/kg or less, 0.90 kJ/kgor less, 0.85 kJ/kg or less, 0.80 kJ/kg or less, 0.75 kJ/kg or less,0.70 kJ/kg or less, 0.65 kJ/kg, or less, 0.60 kJ/kg or less, 0.55 kJ/kgor less, 0.50 kJ/kg or less, 0.45 kJ/kg or less, 0.40 kJ/kg or less,0.35 kJ/kg or less, 0.30 kJ/kg or less, 0.25 kJ/kg or less, 0.20 kJ/kgor less, or 0.15 kJ/kg or less) to the surfactant composition and theaqueous fluid.

The single stage mixing process can comprise applying a specific mixingenergy to the surfactant composition and the aqueous fluid ranging fromany of the minimum values described above to any of the maximum valuesdescribed above. For example; in some embodiments, the single stagemixing process can comprise applying a specific mixing energy of from0.10 kJ/kg to 1.50 kJ/kg (e.g., from 0.15 kJ/kg to 1.40 kJ/kg, from 0.15kJ/kg, to 1.20 kJ/kg) to the surfactant composition and the aqueousfluid.

The surfactant composition can be combined with an aqueous fluid in abatch process or a continuous process. In certain embodiments, thesurfactant composition is combined with an aqueous fluid in a continuousprocess. For example, the surfactant composition can be combined with anaqueous fluid as a continuous process to produce a fluid stream forinjection into a hydrocarbon-beating formation. A continuous process isa process that can be effected without the need to be intermittentlystopped or slowed. For example, continuous processes can meet one ormore of the following criteria: (a) materials for forming the aqueouspolymer solution (e.g., the surfactant composition and the aqueousfluid) are fed into the system in which the aqueous surfactant-polymersolution is produced at the same rate as the aqueous surfactant-polymersolution is removed from the system; (b) the nature of thecomposition(s) introduced to the system in which the aqueoussurfactant-polymer solution is produced is a function of thecomposition(s) position with the process as it flows from the point atwhich the composition(s) are introduced to the system to the point atwhich the aqueous surfactant-polymer solution is removed from thesystem; and/or (c) the quantity of aqueous surfactant-polymer solutionproduced is a function of (i) the duration for which the process isoperated and (ii) the throughput rate of the process.

As discussed above, methods for preparing an aqueous surfactant-polymersolution from a surfactant composition can comprise combining thesurfactant composition with an aqueous fluid in a single stage mixingprocess. As used herein, the phase “single stage mixing process” refersto mixing processes where a surfactant composition and an aqueous fluidare combined in their final proportions either before mixing or within afirst mixer, such that the fluid exiting the first mixer includes allcomponents of the final aqueous surfactant-polymer solution at theirfinal concentration. Optionally, the fluid exiting the first mixer canundergo additional mixing steps; however, additional volumes of thesurfactant composition or the aqueous fluid are not added once the fluidexits the first mixer. In this context; single stage mixing processescan be distinguished from conventional dual-stage and multistage mixingprocesses. Dual-stage and multistage mixing processes generally wouldinvolve the combination of a surfactant composition and an aqueous fluideither before mixing or within a first mixer to produce a concentratedcomposition, which must then be diluted with additional aqueous fluidafter leaving the first mixer to produce a fluid that includes all ofthe components of the final aqueous surfactant-polymer solution at theirfinal concentrations.

The single stage mixing process can comprise a single mixing step; or aplurality of mixing steps (i.e., two or more steps). In single stagemixing processes that comprise a single mixing step, a surfactantcomposition and an aqueous fluid are combined in their final proportions(either before mixing or within a first mixer), mixed within a firstmixer, and exit the first mixer as an aqueous surfactant-polymersolution. For example, a polymer feed stream comprising the surfactantcomposition can be combined (e.g., in a fixed ratio) with an aqueousfluid stream upstream of or within an in-line mixer. The combined fluidstream can then pass through the in-line mixer, emerging as the aqueoussurfactant-polymer solution. In some embodiments, the in-line mixer canhave a mixer inlet and a mixer outlet, and the difference in pressurebetween the mixer inlet and the mixer outlet can be from 15 psi to 400psi (e.g., from 15 psi to 150 psi, from 15 psi to 100 psi, or from 15psi to 75 psi).

An example system for the preparation of an aqueous surfactant-polymersolution in a single mixing step is illustrated schematically in FIG. 18. As shown in FIG. 18 , a pump 102 can be used to inject a stream of thesurfactant composition 104 into a line 106 carrying the aqueous fluidstream. The combined fluid stream can then pass through an in-line mixer108 having a mixer inlet 110 and a mixer outlet 112; emerging as theaqueous surfactant-polymer solution. The pressure drop through thein-line mixer 108 (Δp) can be from 15 psi to 400 psi (e.g., from 15 psito 150 psi, from 15 psi to 100 psi, or from 15 psi to 75 psi).

In other embodiments, the single stage mixing process comprise two ormore mixing steps (e.g., a first mixing step in which a surfactantcomposition and an aqueous fluid are combined in their final proportions(either before mixing or within a first mixer), mixed within a firstmixer, and exit the first mixer as a partially mixed aqueoussurfactant-polymer solution; and one or more additional mixing steps inwhich the partially mixed aqueous surfactant-polymer solution is mixedwithin one or more additional mixers to produce the final aqueoussurfactant-polymer solution). For example, the single stage mixingprocess can comprise two, three, four, five, or more consecutive mixingsteps. In certain cases, the single stage mixing process can comprisetwo mixing steps.

An example system for the preparation of an aqueous surfactant-polymersolution in two mixing steps is illustrated schematically in FIG. 19 ,As shown in FIG. 19 , pumps 102 can be used to inject a stream of thesurfactant composition 104 and a stream of aqueous fluid 106 through afirst in-line mixer 108 having a first mixer inlet 110 and a first mixeroutlet 112, emerging as a stream of partially mixed aqueoussurfactant-polymer solution 114. The partially mixed aqueoussurfactant-polymer solution can comprise a concentration of synthetic(co)copolymer of from 50 to 15,000 ppm (e.g., from 500 to 5000 ppm, orfrom 500 to 3000 ppm). The pressure drop through the first in-line mixer108 (Δp1) can be from 15 psi to 400 psi (e.g., from 15 psi to 150 psi,from 15 psi to 100 psi, or from 15 psi to 75 psi). The stream ofpartially mixed aqueous surfactant-polymer solution 114 can then passthrough a second in-line mixer 116 having a second mixer inlet 118 and asecond mixer outlet 120, emerging as a stream of aqueoussurfactant-polymer solution 122. The pressure drop through the secondin-line mixer 116 (Δp2) can be from 15 psi to 400 psi (e.g., from 15 psito 150 psi, from 15 psi to 100 psi, or from 15 psi to 75 psi). In someembodiments, the first in-line mixer can comprise a static mixer and thesecond in-line mixer can comprise a static mixer. In other examples, thefirst in-line mixer can comprise a static mixer and the second in-linemixer can comprise a dynamic mixer.

In some embodiments, the single stage mixing process for preparing anaqueous surfactant-polymer solution can comprise parallel single mixingsteps, parallel multiple mixing steps, or a combination thereof. Anexample system for the preparation of an aqueous surfactant-polymersolutions using parallel mixing steps (e.g., parallel single mixingsteps, parallel multiple mixing steps, or a combination thereof) isillustrated schematically in FIG. 20 . As shown in FIG. 20 , a pump 102can be used to direct a stream of the surfactant composition 104 to asurfactant composition manifold (SC manifold, 122). SC manifold 122 caninclude an SC manifold inlet 124 through which the surfactantcomposition enters the SC manifold 122, and a plurality of SC manifoldoutlets 126 (in this example three manifold outlets) through whichstreams of the surfactant composition exit the SC manifold 122. Thesystem can also include a main line 103 carrying an aqueous fluid streamto aqueous fluid manifold 128. The aqueous fluid manifold 128 caninclude an aqueous fluid manifold inlet 130 through which the aqueousfluid enters the aqueous fluid manifold 128, and a plurality of aqueousfluid manifold outlets 132 (in this example three manifold outlets)through which streams of the aqueous fluid exit the aqueous fluidmanifold 128. Each stream of surfactant composition exiting SC manifold122 can then be combined with a stream of aqueous fluid exiting theaqueous fluid manifold 128 in a different configuration of in-linemixers 134, thereby forming a plurality of streams of the aqueoussurfactant-polymer solution in parallel. Each configuration of in-linemixers 134 can include, independently, a single in-line mixer or aplurality of in-line mixers fluidly connected in series (e.g., as shownin FIGS. 1 and 2 ). By selecting appropriate configurations of in-linemixers 134, system for the preparation of an aqueous polymer solutionsthat employ parallel single steps, parallel multiple steps, or anycombination thereof can be readily fabricated.

In some embodiments, the single stage mixing process can compriseparallel single mixing steps, parallel multiple mixing steps, or acombination thereof that are carried out in a polymer mixing system. Incertain examples, the mixing system can be positioned subsea. Examplepolymer mixing systems that can be used to conduct a single stage mixingprocess comprising parallel single mixing steps are schematicallyillustrated in FIGS. 21A and 21B. As shown in FIG. 21A, the system caninclude a main polymer feed line 202 diverging to a plurality of polymersupply branches 204, a main aqueous feed line 206 diverging to aplurality of aqueous supply branches 208, and a plurality of mixerarrangements 210 (only one of which is illustrated in FIG. 21A forclarity). In other examples, as shown in FIG. 21B, the main polymer feedline 202 can be fluidly connected to the plurality of polymer supplybranches 204 via a polymer distribution manifold 224. The polymerdistribution manifold 224 can be configured to independently control thefluid flow rate through each of the plurality of polymer supply branches204.

Referring again to FIG. 21A, each of the plurality of mixer arrangements210 is supplied by one of the plurality of polymer supply branches 204and one of the plurality of aqueous supply branches 208. Each of theplurality of mixer arrangements 210 can comprise an in-line mixer 212having a mixer inlet 214 and a mixer outlet 216.

Optionally, the mixing system can further comprise a flow control valve220 operably coupled to each the plurality of polymer supply branches204 to control fluid flow rate through each of the plurality of polymersupply branches. Optionally, the mixing system can further comprise aflow control valve 222 operably coupled to each the plurality of aqueoussupply branches 208 to control fluid flow rate through each of theplurality of aqueous supply branches. In certain embodiments, the mixingsystem can further comprise a flow control valve 220 operably coupled toeach the plurality of polymer supply branches 204 to control fluid flowrate through each of the plurality of polymer supply branches, and aflow control valve 222 operably coupled to each the plurality of aqueoussupply branches 208 to control fluid flow rate through each of theplurality of aqueous supply branches. Examples of suitable flow controlvalves include, for example, choke valves, chemical injection meteringvalves (CIMVs), and control valves.

Referring still to FIG. 21A, the surfactant composition and the aqueousfluid can be combined in the polymer mixing system by passing thesurfactant polymer composition through the main polymer feed line 202and the plurality of polymer supply branches 204 to reach each of theplurality of mixer arrangements 210. The surfactant composition and theaqueous fluid can then flow through the in-line mixer 212 of each of theplurality of mixer arrangements 210 to provide a stream of the aqueoussurfactant-polymer solution 218. The pressure drop through the in-linemixer 212 (Sp) can be from 15 psi to 400 psi (e.g., from 15 psi to 150psi, from 15 psi to 100 psi, or from 15 psi to 75 psi). In someembodiments, the surfactant composition and the aqueous fluid can flowthrough the in-line mixer 212 of each of the plurality of mixerarrangements 210 at a velocity of from 1 m/s to 4 m/s.

Example mixing systems that can be used to conduct a single stage mixingprocess comprising parallel multiple mixing steps are schematicallyillustrated in FIGS. 22A and 2B. As shown in FIG. 22A, the system caninclude a main polymer feed line 302 diverging to a plurality of polymersupply branches 304, a main aqueous feed line 306 diverging to aplurality of aqueous supply branches 308, and a plurality of mixerarrangements 310 (only one of which is illustrated in FIG. 2A forclarity). In other examples, as shown in FIG. 2B, the main polymer feedline 302 can be fluidly connected to the plurality of polymer supplybranches 304 via a polymer distribution manifold 332. The polymerdistribution manifold 332 can be configured to independently control thefluid flow rate through each of the plurality of polymer supply branches304.

Referring again to FIG. 2A, each of the plurality of mixer arrangements310 is supplied by one of the plurality of polymer supply branches 304and one of the plurality of aqueous supply branches 308. Each of theplurality of mixer arrangements 310 can comprise a first in-line mixer312 having a first mixer inlet 314 and a first mixer outlet 316 inseries with a second in-line mixer 318 having a second mixer inlet 320and a second mixer outlet 322.

Optionally, the mixing system can further comprise a flow control valve324 operably coupled to each the plurality of polymer supply branches304 to control fluid flow rate through each of the plurality of polymersupply branches. Optionally, the mixing system can further comprise aflow control valve 326 operably coupled to each the plurality of aqueoussupply branches 308 to control fluid flow rate through each of theplurality of aqueous supply branches. In certain embodiments, the mixingsystem can further comprise a flow control valve 324 operably coupled toeach the plurality of polymer supply branches 304 to control fluid flowrate through each of the plurality of polymer supply branches, and aflow control valve 326 operably coupled to each the plurality of aqueoussupply branches 308 to control fluid flow rate through each of theplurality of aqueous supply branches. Examples of suitable flow controlvalves include, for example, choke valves, chemical injection meteringvalves (CIMVs), and control valves.

Referring still to FIG. 22A, the surfactant composition and the aqueousfluid can be combined in the mixing system by passing the surfactantcomposition through the main polymer feed line 302 and the plurality ofpolymer supply branches 304 to reach each of the plurality of mixerarrangements 310. The surfactant composition and the aqueous fluid canthen flow through the through a first in-line mixer 312 having a firstmixer inlet 314 and a first mixer outlet 316, emerging as a stream ofpartially mixed aqueous surfactant-polymer solution 328. The partiallymixed aqueous surfactant-polymer solution can comprise a concentrationof synthetic (co)copolymer of from 50 to 15,000 ppm (e.g., from 500 to5000 ppm, or from 500 to 3000 ppm). The pressure drop through the firstin-line mixer 312 (Δp1) can be from 15 psi to 400 psi (e.g., from 1:5psi to 150 psi, from 15 psi to 100 psi, or from 15 psi to 75 psi), Insome embodiments, the surfactant composition and the aqueous fluid canflow through the first in-line mixer 312 of each of the plurality ofmixer arrangements 310 at a velocity of from 1 m/s to 4 m/s. The streamof partially mixed aqueous surfactant-polymer solution 328 can then passthrough a second in-line mixer 318 having a second mixer inlet 320 and asecond mixer outlet 322, emerging as a stream of aqueous polymersolution 330. The pressure drop through the second in-line mixer 318(Δp2) can be from 15 psi to 400 psi (e.g., from 15 psi to 150 psi, from15 psi to 100 psi, or from 15 psi to 75 psi). In some embodiments, thepartially mixed aqueous surfactant-polymer solution 328 can flow throughthe second in-line mixer 318 of each of the plurality of mixerarrangements 310 at a velocity of from 1 m/s to 4 m/s. In someembodiments, the first in-line mixer can comprise a static mixer and thesecond in-line mixer can comprise a static mixer. In other examples, thefirst in-line mixer can comprise a static mixer and the second in-linemixer can comprise a dynamic mixer.

Any suitable in-line mixer(s) can be used in conjunction with themethods and systems described above. Each in-line mixer can be a dynamicmixer or a static mixer. Suitable dynamic mixers, which involvemechanical agitation of one type or another, are known in the art, andinclude impeller mixers, turbine mixers, rotor-stator mixers, colloidmills, pumps, and pressure homogenizers. In certain embodiment, thein-line mixer(s) can comprise a dynamic mixer such as an electricalsubmersible pump, hydraulic submersible pump, or a progressive cavitypump. In certain embodiments, the in-line mixer(s) can comprise staticmixers. Static mixers are mixers that mix fluids in flow without the useof moving parts. Static mixers are generally constructed from a seriesof stationary, rigid elements that form intersecting channels to split,rearrange and combine component streams resulting in one homogeneousfluid stream. Static mixers provide simple and efficient solutions tomixing and contacting problems. More affordable than dynamic agitatorsystems, static mixing units have a long life with minimal maintenanceand low pressure drop. Static mixers can be fabricated from metalsand/or plastics to fit pipes and vessels of virtually any size andshape. In some cases, the static mixer can comprise a region of pipe,for example a serpentine region of pipe that facilitates mixing.

The aqueous fluid combined with the surfactant composition can comprisefrom 0 to 250,000 ppm; 15,000 to 160,000 ppm; from 15,000 to 100,000ppm; from 10,000 to 50,000 ppm; from 15,000 to 50,000 ppm; from 30,000to 40,000 ppm; from 10,000 to 25,000 ppm; from 10,000 to 20,000 ppm; orfrom 15,000 to 16,000 ppm total dissolved solids (tds). In an exampleembodiment, the aqueous fluid can comprise a brine having about 15.000ppm tds. In one embodiment, the brine may be a synthetic seawater brineas illustrated in the table below.

Composition of an Example Synthetic Seawater Brine Ions (ppm) SyntheticSeawater Brine Na+ 10800 K+ 400 Ca++ 410 Mg++ 1280 Cl− 19400 TDS 32290

The aqueous fluid combined with the surfactant compositions can compriseproduced reservoir brine, reservoir brine, sea water, fresh water,produced water, water, saltwater (e.g. water containing one or moresalts dissolved therein), brine, synthetic brine, synthetic seawaterbrine, or any combination thereof. Generally, the aqueous fluid cancomprise water from any, readily available source, provided that it doesnot contain an excess of compounds that may adversely affect othercomponents in the aqueous surfactant-polymer solution or render theaqueous surfactant-polymer solution unsuitable for its intended use(e.g., unsuitable for use in an oil and gas operation such as an EORoperation). If desired, aqueous fluids obtained from naturally occurringsources can be treated prior to use. For example, aqueous fluids can besoftened (e.g., to reduce the concentration of divalent and trivalentions in the aqueous fluid) or otherwise treated to adjust theirsalinity. In certain embodiments, the aqueous fluid can comprise softbrine or hard brine. In certain embodiments, the aqueous fluid cancomprise produced reservoir brine, reservoir brine, sea water, or acombination thereof.

In one embodiment, seawater is used as the aqueous fluid, sinceoff-shore production facilities tend to have an abundance of seawateravailable, limited storage space, and transportation costs to and froman off-shore site are typically high. If seawater is used as the aqueousfluid, it can be softened prior to the addition of the suspendedpolymer, thereby removing multivalent ions in the water (e.g.,specifically Mg²⁺ and Ca²⁺).

In some embodiments, the aqueous fluid can have a temperature of from 1°C. to 1.20° C. In other embodiments, the aqueous fluid can have atemperature of from 45° C. to 95° C.

The methods described herein can be specifically adapted for use in aparticular oil and gas operation. For example, in some embodiments, theprocesses for preparing aqueous polymer solutions described herein canbe performed as a continuous process to produce a fluid stream forinjection into a hydrocarbon-bearing formation.

In some cases, the in-line mixer (or one or more in-line mixers in thecase of methods that include multiple mixing steps, parallel singlemixing steps, or parallel multiple mixing steps) can be arrangeddownstream from pumping equipment at the surface (e.g., on land, on avessel, or on an offshore platform) that pumps the surfactantcomposition and the aqueous fluid. In certain embodiments, the in-linemixer (or one or more in-line mixers in the case of methods that includemultiple mixing steps, parallel single mixing steps, or parallelmultiple mixing steps) can be positioned at or near the wellhead of awell. In certain embodiments, the in-line mixer can be arrangeddownhole. In certain embodiments, the in-line mixer (or one or morein-line mixers in the case of methods that include multiple mixingsteps, parallel single mixing steps, or parallel multiple mixing steps)can be positioned subsurface, subsea, or downhole.

In certain embodiments, the hydrocarbon-bearing formation can be asubsea reservoir. In these embodiments, the in-line mixer (or one ormore in-line mixers in the case of methods that include multiple mixingsteps, parallel single mixing steps, or parallel multiple mixing steps)can be arranged downstream from pumping equipment at the surface (e.g.,on shore, on a vessel, or on an offshore platform) that pumps thesurfactant composition and/or the aqueous fluid. In certain embodiments,the in-line mixer (or one or more in-line mixers in the case of methodsthat include multiple mixing steps, parallel single mixing steps, orparallel multiple mixing steps) can be positioned subsea. Thus,depending on the oil and gas operation, for example, an in-line mixercan be positioned on the surface, subsurface, subsea, or downhole.

As discussed above, the aqueous polymer solutions described herein canbe used oil and gas operations, such as EOR operations. For example, theaqueous surfactant-polymer solutions described above can be used inflooding operations. In some cases, the aqueous polymer solution furtherincludes one or more additional agents to facilitate hydrocarbonrecovery. For example, the aqueous polymer solution can further includean alkalinity agent, a chelating agent, or any combination thereof. Assuch, the aqueous surfactant-polymer solutions can be used in polymer(P), alkaline-polymer (AP), surfactant-polymer (SP), and/or inalkaline-surfactant-polymer (ASP)-type EOR operations. When present,these additional components can be incorporated into the aqueous fluidprior to combination with the surfactant composition, such that theresulting aqueous surfactant-polymer solution formed by combination ofthe aqueous fluid and the surfactant composition includes one or more ofthese additional components. Likewise, these additional components canalso be incorporated to the surfactant composition prior to combinationwith the aqueous fluid, such that the resulting aqueoussurfactant-polymer solution formed by combination of the aqueous fluidand the surfactant composition includes one or more of these additionalcomponents. Alternatively, these additional components can beincorporated to the aqueous surfactant-polymer solutions followingcombination with the surfactant composition.

For chemical enhanced oil recovery (CEOR) operations, the surfactantcomposition can be combined with an effective amount of aqueous fluid toprovide an aqueous surfactant-polymer solution (e.g., which can serve asan injection stream) with a target hydrated polymer concentration andparticle size. The target concentration varies according to the type ofpolymer employed, as well as the characteristics of the reservoir, e.g.,petrophysical rock properties, reservoir fluid properties, reservoirconditions such as temperature, permeability, water compositions,mineralogy and/or reservoir location, etc. In some cases, the aqueoussurfactant-polymer solutions described herein are suitable for use inreservoirs with a permeability of from 10 millidarcy to 40,000millidarcy.

The hydrated polymer molecules in the aqueous surfactant-polymersolution can have a particle size (radius of gyration) ranging from 0.01to 10 μm in one embodiment. One reservoir characteristic is the medianpore throats, which correspond to the permeability of the reservoirs.Depending on the reservoir, the median pore throats in reservoirs mayrange from 0.01 μm to several hundred micrometers. Since the size ofhydrated polymers in water range from 0.01 micrometer to severalmicrometers depending on the species, molecules, and reservoirconditions, in one embodiment, appropriate polymers are selected forsurfactant composition to afford an aqueous surfactant-polymer solutionwhere the particle size of the hydrated polymer is <10% of the medianpore throat parameters. This can allow the hydrated polymer particles toflow through the porous medium in an uninhibited manner. In anotherembodiment, the hydrated polymer particles have an average particle sizeranging from 2 to 8% of the median pore throat size. Surfactants can beincluded to lower the interfacial tension between the oil and waterphase to less than about 10−2 dyne/cm (for example) and thereby recoveradditional oil by mobilizing and solubilizing oil trapped by capillaryforces.

Suitable alkalinity agents include basic, ionic salts of alkali metalsor alkaline earth metals. Alkalinity agents can be capable of reactingwith an unrefined petroleum acid (e.g. the acid or its precursor incrude oil (reactive oil)) to form soap (a surfactant which is a salt ofa fatty acid) in situ. These in situ generated soaps can serve as asource of surfactants causing a reduction of the interfacial tension ofthe oil in water emulsion, thereby reducing the viscosity of theemulsion. Examples of alkali agents include alkali metal hydroxides,carbonates, or bicarbonates, including; but not limited to, sodiumcarbonate, sodium bicarbonate, sodium hydroxide, potassium hydroxide,sodium silicate, tetrasodium EDTA, sodium metaborate, sodium citrate,and sodium tetraborate. In some cases, the alkalinity agent can bepresent in the inverted polymer solution in an amount of from 0.3 to 5.0weight percent of the solution, such as 0.5 to 3 weight percent.

The aqueous surfactant-polymer solution can optionally include a chelantor chelating agent. Chelants may be used to complex with the alkalimetal and soften brines. If desired, the salinity of the aqueous polymersolution may be optimized for a particular subterranean reservoir byadjusting a number of chelating ligands in the chelating agent, such asalkoxylate groups if the chelant is EDTA (“ethylenediaminetetraaceticacid”). EDTA is just one example of a suitable chelant, another exampleof a chelant is MGDA (“methylglycinediacetic acid”).

If desired, other additives can also be included in aqueoussurfactant-polymer solutions described herein, such as biocides, oxygenscavengers, and corrosion inhibitors.

Variants of the methods described above can also be used to prepareaqueous p surfactant-polymer solutions that include biopolymers, such aspolysaccharides (e.g., xanthan gum, scleroglucan, guar gum, derivativesthereof including one or more chemical modifications to the backbone ofthese polymers, and blends thereof). These methods can compriseproviding a surfactant composition that comprises an LP compositioncomprising one or more biopolymers; and combining the surfactantcomposition with an aqueous fluid in a single stage mixing processdescribed above to provide the aqueous surfactant-polymer solution,wherein the aqueous surfactant-polymer solution comprises aconcentration of biopolymer of from 50 to 15,000 ppm; and wherein theaqueous surfactant-polymer solution has a filter ratio of 1.5 or less at15 psi using a 1.2 μm filter.

In methods used to prepare aqueous surfactant-polymer solutions thatinclude biopolymers, the single stage mixing process can compriseapplying a specific mixing energy of at least 0.10 kJ/kg to thesurfactant composition and the aqueous fluid.

In some of these embodiments, the single stage mixing process cancomprise applying a specific mixing energy of at least 0.10 kJ/kg (e.g.,at least 0.25 kJ/kg, at least 0.50 kJ/kg, at least 0.75 kJ/kg, at least1.0 kJ/kg, at least 1.5 kJ/kg, at least 2.0 kJ/kg, at least 2.5 kJ/kg,at least 3.0 kJ/kg, at least 3.5 kJ/kg, at least 4.0 kJ/kg, at least 4.5kJ/kg, at least 5.0 kJ/kg, at least 6.0 kJ/kg, at least 7.0 kJ/kg, atleast 8.0 kJ/kg, at least 9.0 kJ/kg, at least 10 kJ/kg, at least 11kJ/kg, at least 12 kJ/kg, at least 13 kJ/kg, at least 14 kJ/kg, at least15 kJ/kg, at least 16 kJ/kg, at least 17 kJ/kg, at least 18 kJ/kg, or atleast 19 kJ/kg) to the surfactant composition and the aqueous fluid. Insome of these embodiments, the single stage mixing process can compriseapplying a specific mixing energy of 20 kJ/kg or less (e.g., 19 kJ/kg orless, 18 kJ/kg or less, 17 kJ/kg or less, 16 kJ/kg or less, 15 kJ/kg orless, 14 kJ/kg or less, 13 kJ/kg or less, 12 kJ/kg or less, 11 kJ/kg orless, 10 kJ/kg or less, 9.0 kJ/kg or less, 8.0 kJ/kg or less, 7.0 kJ/kgor less, 6.0 kJ/kg or less, 5.0 kJ/kg or less, 4.5 kJ/kg, or less, 4.0kJ/kg or less, 3.5 kJ/kg or less, 3.0 kJ/kg or less, 2.5 kJ/kg or less,2.0 kJ/kg or less, 1.5 kJ/kg or less, 1.0 kJ/kg or less, 0.75 kJ/kg orless, 0.50 kJ/kg or less, or 0.25 kJ/kg or less) to the surfactantcomposition and the aqueous fluid.

In some of these embodiments, the single stage mixing process cancomprise applying a specific mixing energy to the surfactant compositionand the aqueous fluid ranging from any of the minimum values describedabove to any of the maximum values described above. For example, in someof these embodiments, the single stage mixing process can compriseapplying a specific mixing energy of from 0.10 kJ/kg to 20 kJ/kg. (e.g.,from 0.10 kJ/kg to 10 kJ/kg, from 1.0 kJ/kg to 20 kJ/kg, from 1.0 kJ/kgto 15 kJ/kg, from 1.0 kJ/kg to 10 kJ/kg, or from 5.0 kJ/kg to 15 kJ/kg)to the surfactant composition and the aqueous fluid.

Methods of Use

The aqueous surfactant-polymer solutions described herein can be used ina variety of oil and gas operations, including an EOR operation (e.g.,an improved oil recovery (IOR) operation, a polymer flooding operation,an AP flooding operation, a SP flooding operation, an ASP floodingoperation, a conformance control operation, or any combination thereof).Moreover, the aqueous surfactant polymer solutions described herein canbe used in a variety of oil and gas operations, including a hydraulicfracturing operation, as a drag reducer that reduces friction duringtransportation of a fluid in a pipeline, or any combination thereof.Transportation of a fluid in a pipeline can refer to any movement of afluid through a conduit or pipe. As such, transportation of a fluid in apipeline includes, for example, the pipeline transport of fluids as wellas passage of fluids through pipes such as wellbores during the courseof an oil recovery operation. The aqueous surfactant polymer solutionscan even be used in water treatment operations associated with oil andgas operations.

In one embodiment, the aqueous surfactant-polymer solution can be usedas an injection fluid. In another embodiment, the aqueoussurfactant-polymer solution can be included in an injection fluid. Inanother embodiment, aqueous surfactant-polymer solution can be used as ahydraulic fracturing fluid. In another embodiment, the aqueoussurfactant-polymer solution can be included in a hydraulic fracturingfluid. In another embodiment, the aqueous surfactant-polymer solutioncan be used as a drag reducer that reduces friction duringtransportation of a fluid in a pipeline. In another embodiment, theaqueous surfactant-polymer solution can be included in a drag reducerthat reduces friction during transportation of a fluid in a pipeline. Inshort, in certain embodiments, the aqueous surfactant-polymer solutionsdescribed herein can be used in hydrocarbon recovery.

Methods of hydrocarbon recovery can comprise providing a subsurfacereservoir containing hydrocarbons therewithin; providing a wellbore influid communication with the subsurface reservoir; preparing an aqueoussurfactant-polymer solution using the methods described above; andinjecting the aqueous surfactant-polymer solution through the wellboreinto the subsurface reservoir. For example, the subsurface reservoir canbe a subsea reservoir and/or the subsurface reservoir can have apermeability of from 10 millidarcy to 40,000 millidarcy.

The wellbore in the second step can be an injection wellbore associatedwith an injection well, and the method can further comprise providing aproduction well spaced-apart from the injection well a predetermineddistance and having a production wellbore in fluid communication withthe subsurface reservoir. In these embodiments, injection of the aqueoussurfactant-polymer solution can increase the flow of hydrocarbons to theproduction wellbore.

In some embodiments, methods of hydrocarbon recovery can further includea recycling step. For example, in some embodiments, methods ofhydrocarbon recovery can further comprise producing production fluidfrom the production well, the production fluid including at least aportion of the injected aqueous surfactant-polymer solution; andcombining the production fluid to with additional surfactantcomposition, for example, to form a second aqueous surfactant-poly triersolution. The second aqueous surfactant-polymer solution can then beinjected into at least one wellbore (e.g., an injection well, the samewellbore discussed in the second step or a different wellbore, etc.).Thus, in some embodiments, the aqueous surfactant-polymer solution isincluded in an injection fluid.

The wellbore in the second step can be a wellbore for hydraulicfracturing that is in fluid communication with the subsurface reservoir.Thus, in one embodiment, the aqueous surfactant-polymer solutioninjected in the fourth step functions as a drag reducer that reducesfriction during injection in the fourth step. By doing so, the aqueoussurfactant-polymer solution is used as a drag reducer that reducesfriction during transportation of a fluid (e.g., the hydraulicfracturing fluid) in a pipeline (e.g., the wellbore or componentsthereof). In another embodiment, the aqueous surfactant-polymer solutionis included in a hydraulic fracturing fluid.

In other embodiments, the aqueous surfactant-polymer solution can beused in methods for wellbore remediation, such as those described inU.S. Pat. No. 9,752,071 to Dwarakanath et al., which is incorporatedherein by reference in its entirety. Accordingly, also provided aremethods for the remediation of existing damage in a region near aninjection wellbore in communication with a subterranean reservoirwherein the injection wellbore is not intended for receivinghydrocarbons and wherein the existing damage is caused by previousinjection of a composition containing a polymer emulsion into theinjection wellbore, which comprise preparing an aqueoussurfactant-polymer solution according to the methods described herein,and injecting the aqueous surfactant-polymer solution through theinjection wellbore into the subsurface reservoir, thereby dissolving,cleaning and/or flushing the polymer emulsion away from the injectionwellbore. The injection of the composition can stimulate the region nearthe injection wellbore in communication with the subterranean reservoir.The injection can improve the relative permeability of the region nearthe injection wellbore in communication with the subterranean reservoir.For example, the relative permeability of the region near the injectionwellbore in communication with the subterranean reservoir can beincreased by at least 250 percent.

Also provided are methods for increasing the relative permeability of aregion near an injection wellbore in communication with a subterraneanreservoir, wherein the injection wellbore is not intended for receivinghydrocarbons, which comprise preparing an aqueous surfactant-polymersolution according to the methods described herein, and injecting theaqueous surfactant-poly trier solution through the injection wellboreinto the subsurface reservoir. The region near the injection wellborecan comprise a substance chosen from a heavy oil, a polymer, a drillingfluid, a drilling mud, or any combination thereof, and wherein injectingthe aqueous surfactant-polymer solution through the injection wellboreinto the subsurface reservoir can comprise dissolving, cleaning and/orflushing the substance away from the injection wellbore. The injectioncan improve the relative permeability of the region near the injectionwellbore in communication with the subterranean reservoir. For example,the relative permeability of the region near the injection wellbore incommunication with the subterranean reservoir can be increased by atleast 250 percent.

In some embodiments, the aqueous surfactant-polymer solution can be usedas part of a completion and/or fracturing operation. For example, theaqueous surfactant-polymer solution can be injected into anunconventional subterranean formation to form and/or extend fractureswithin the formation. In certain embodiments, the fracturing operationcan comprise injecting the aqueous surfactant-polymer solution through awellbore and into the unconventional subterranean formation at asufficient pressure and at a sufficient rate to fracture theunconventional subterranean formation. In some embodiments, the wellboreis a hydraulic fracturing wellbore associated with a hydraulicfracturing well, for example, that may have a substantially verticalportion only, or a substantially vertical portion and a substantiallyhorizontal portion below the substantially vertical portion. In someembodiments, the fracturing operation can be performed in a new well(e.g., a well that has not been previously fractured). In otherembodiments, the aqueous surfactant-polymer solution can be used in afracturing operation in an existing well (e.g., in a refracturingoperation).

In some embodiments, the method can comprise performing a fracturingoperation on a region of the unconventional subterranean formationproximate to a new wellbore. In some embodiments, the method cancomprise performing a fracturing operation on a region of theunconventional subterranean formation proximate to an existing wellbore.In some embodiments, the method can comprise performing a refracturingoperation on a previously, fractured region of the unconventionalsubterranean formation proximate to a new wellbore. In some embodiments,the method can comprise performing a refracturing operation on apreviously fractured region of the unconventional subterranean formationproximate to an existing wellbore. In some embodiments, the method cancomprise performing a fracturing operation on a naturally fracturedregion of the unconventional subterranean formation proximate to a newwellbore (e.g., an infill well). In some embodiments, the method cancomprise performing a fracturing operation on a naturally fracturedregion of the unconventional subterranean formation proximate to anexisting wellbore.

In cases where the fracturing method comprises a refracturing methods,the previously fractured region of the unconventional reservoir can havebeen fractured by any suitable type of fracturing operation. Forexample, the fracturing operation may include hydraulic fracturing,fracturing using electrodes such as described in U.S. Pat. Nos.9,890,627, 9,840,898, U.S. Patent Publication No. 2018/0202273, orfracturing with any other available equipment or methodology. In someembodiments, the fracturing operation can further comprise adding atracer to the aqueous surfactant-polymer solution prior to introducingthe aqueous surfactant-polymer solution through the wellbore into theunconventional subterranean formation; recovering the tracer from thefluids produced from the unconventional subterranean formation throughthe wellbore, fluids recovered from a different wellbore in fluidcommunication with the unconventional subterranean formation, or anycombination thereof; and comparing the quantity of tracer recovered fromthe fluids produced to the quantity of tracer introduced to the aqueoussurfactant-polymer solution. The tracer can comprise a proppant tracer,an oil tracer, a water tracer, or any combination thereof. Exampletracers are known in the art, and described, for example, in U.S. Pat.No. 9,914,872 and Ashish Kumar et al., Diagnosing Fracture-WellboreConnectivity Using Chemical Tracer Flowback Data, URTeC 2902023, Jul.23-25, 2018, page 1-10, Texas, USA.

The aqueous surfactant-polymer solution can be used at varying pointsthroughout a fracturing operation. For example, the aqueoussurfactant-polymer solution can be used as an injection fluid during thefirst, middle or last part of the fracturing process, or throughout theentire fracturing process. In some embodiments, the fracturing processcan include a plurality of stages and/or sub-stages. For example, thefracturing process can involve sequential injection of fluids indifferent stages, with each of the stages employing a differentaqueous-based injection fluid system (e.g., with varying properties suchas viscosity, chemical composition, etc.). Example fracturing processesof this type are described, for example, in U.S. Patent ApplicationPublication Nos. 2009/0044945 and 2015/0083420, each of which is herebyincorporated herein by reference in its entirely.

In these embodiments, the aqueous surfactant-polymer solution can beused as an injection fluid (optionally with additional components)during any or all of the stages and/or sub-stages. Stages and/orsub-stages can employ a wide variety of aqueous-based injection fluidsystems, including linear gels, crosslinked gels, and friction-reducedwater. Linear gel fracturing fluids are formulated with a wide array ofdifferent polymers in an aqueous base. Polymers that are commonly usedto formulate these linear gels include guar, hydroxypropyl guar (HPG),carboxymethyl HPG (CMHPG), and hydroxyethyl cellulose (HEC). Crosslinkedgel fracturing fluids utilize, for example, borate ions to crosslink thehydrated polymers and provide increased viscosity. The polymers mostoften used in these fluids are guar and HPG. The crosslink obtained byusing borate is reversible and is triggered by altering the pH of thefluid system. The reversible characteristic of the crosslink in boratefluids helps them clean up more effectively, resulting in good regainedpermeability and conductivity. The aqueous surfactant-polymer solutionsdescribed herein can be added to any of these aqueous-based injectionfluid systems.

In some embodiments, the aqueous surfactant-polymer solution can beformed in a continuous process (and then subsequently injected). Inother embodiments, the aqueous surfactant-polymer solution can beprovided only during desired portions of the treatment operation (e.g.,during one or more phases or stages of a fracturing operation). Forexample, the aqueous surfactant-polymer solution could be added wheninjecting slickwater, when injecting fracturing fluid with proppant,during an acid wash, or during any combination thereof. In a specificembodiment, the aqueous surfactant-polymer solution is continuouslyadded to an aqueous injection fluid after acid injection untilcompletion of hydraulic fracturing and completion fluid flow-back. Whenintermittently dosed, the aqueous surfactant-polymer solution can beadded to the aqueous-based injection fluid once an hour, once every 2hours, once every 4 hours, once every 5 hours, once every 6 hours, twicea day, once a day, or once every other day, for example.

In some embodiments, the aqueous surfactant-polymer solution can be usedas part of a reservoir stimulation operation. In such operations, theaqueous surfactant-polymer solution can be injected to alter thewettability of existing fractures within the formation (without furtherfracturing the formation significantly by either forming new fractureswithin the formation and/or extending the existing fractures within theformation). In such stimulation operations, no proppant is used, andfluid injection generally occurs at a lower pressure.

In some cases, the existing fractures can be naturally occurringfractures present within a formation. For example, in some embodiments,the formation can comprise naturally fractured carbonate or naturallyfractured sandstone. The presence or absence of naturally occurringfractures within a subterranean formation can be assessed using standardmethods known in the art, including seismic surveys, geology, outcrops,cores, logging, reservoir characterization including preparing grids,etc.

In some embodiments, methods for stimulating an unconventionalsubterranean formation with a fluid can comprise introducing an aqueoussurfactant-polymer solution through a wellbore into the unconventionalsubterranean formation; allowing the aqueous surfactant-polymer solutionto imbibe into a rock matrix of the unconventional subterraneanformation for a period of time; and producing fluids from theunconventional subterranean formation through the wellbore. In thesemethods, the same wellbore can be used for both introducing the aqueoussurfactant-polymer solution and producing fluids from the unconventionalsubterranean formation. In these methods, the same wellbore can be usedfor both introducing the aqueous surfactant-polymer solution andproducing fluids from the unconventional subterranean formation. In someembodiments, introduction of the aqueous surfactant-polymer solution canincrease the production of hydrocarbons from the same wellbore, from adifferent wellbore in fluid communication with the unconventionalsubterranean formation, or any combination thereof.

By way of non-limiting illustration, examples of certain embodiments ofthe present disclosure are given below.

EXAMPLES

Trapped oil around the immediate vicinity of a wellbore has been removedby selecting suitable low-tension oil mobilizing surfactants mixed withliquid polymers at the desired dosing levels and subsequently injectingthe solution downhole. To accomplish this, one or more concentratedsurfactant streams meet the polymer/brine stream to mix and produce ahomogeneous injection solution for removal of near wellbore trapped oilfor injectivity enhancement or for mobilization of residual oil in thereservoir. Multiple injection streams of different fluids cause thefinal dosing amounts of polymer and surfactant to vary over a wide rangeduring field deployment, resulting in solutions that can fall outside ofthe desired operating range in terms of concentration and injection flowrate. Furthermore, these problems are exacerbated when deployingoffshore due to the need for separate supply vessels, making the effortcost prohibitive and operationally challenging.

To address meet these needs, concentrated surfactant compositions weredeveloped that could be diluted in a single stage mixing process to forman aqueous surfactant-polymer solution for use as an injection fluid inan oil and gas operation. The surfactant compositions include asurfactant package comprising one or more surfactants, one or moreco-solvents, and a liquid polymer (LP) composition. For example, thesurfactant compositions can include from 0.5% to 60% by weight of a LPcomposition, from 0.2% to 98% by weight of a surfactant package, andfrom greater than 0% to 95% by weight of a co-solvent. In addition, thesurfactant composition can also have a water content of from 0.01% to20% by weight (coming from the LP composition and/or the surfactantsthat make up the surfactant package).

The concentrated surfactant composition can be directly diluted with anaqueous fluid (e.g., brine) to produce an aqueous surfactant-polymersolution having the desired concentration of components (e.g., thedesired polymer concentration, the desired surfactant concentration, thedesired co-solvent concentration, or any combination thereof for aparticular oil and gas operation) in a single step. This can eliminatethe need for multiple streams of individual components, therebyimproving process robustness. If desired, the aqueous surfactant-polymersolution can be continuously injected to remove near wellbore trappedoil or injected as a slug to mobilize residual oil in a tertiaryrecovery process. Such a process allows for rapid deployment ofsurfactant polymer flooding processes, especially in offshoreenvironments.

As discussed below, the surfactant compositions described herein can bequickly inverted, hydrated, and mixed in water under strong shearstress. Once diluted, the resulting aqueous surfactant-polymer solutionsexhibit superior filterability after a short hydration time. Thesurfactant compositions exhibit a comparable viscosity yield withconventional liquid polymers. The resulting aqueous surfactant-polymersolutions also exhibit excellent performance in oil recoveryapplications. For example, in coreflood tests, the aqueoussurfactant-polymer solutions can reduce oil saturation in the core toless than 2% after 2 pore volumes (PV) of continuous injection during acleanup recovery coreflood in surrogate rocks and reservoir sand.

The following example surfactant compositions include differentsurfactant classes and types mixed with a liquid polymer (LP)composition at ratios tailored to perform at a temperature and salinitylevel dictated by a chosen end application. Four representativecompositions are described here which can be used for applications innear wellbore cleanup by continuous surfactant polymer cleanupinjection, for enhancing oil recovery by classical surfactant polymerslug injection, and for preparing slickwater used in hydraulicfracturing process.

Table 1 shows the composition of the brine used in these examples whendiluting the concentrated surfactant compositions described herein.

TABLE 1 Synthetic formation brine in this study for dilutions based onformulation 1. ION Concentration (ppm) Na⁺ 5048 Ca²⁺ 569 Mg²⁺ 210 Cl⁻9403 TDS 15230

Surfactant Composition 1

Surfactant Composition 1 was developed for wellbore cleanup as well asto improve oil recovery. The composition described here in Table 2 has aratio of polymer to surfactants/cosolvents of 1:4, The approximate watercontent of the composition is about 6.5%, with the water coming in fromthe individual components used to prepare the composition. FIG. 1A showsthe appearance of the concentrated surfactant composition, and FIG. 1Bshows the aqueous stable 3000 ppm polymer solution made by diluting theconcentrated surfactant composition in brine in a single stage mixingprocess.

TABLE 2 Surfactant Composition 1. Wt. % Wt. % in in diluted aqueousconcentrated surfactant-polymer- surfactant Component polymer solutioncomposition TDA-8PO-Sulfate 0.15 5.5 C20-28 Isomerized olefin sulfonate0.3 11 Sodium Dihexyl Sulfosuccinate 0.5 18.35 Ethylene glycol monobutylether 0.75 27.5 Polymer 0.3 11 Other (Water or brine, oil from 98 26.65polymer and any other components that come with chemicals)

Surfactant Composition 2

This composition (Table 3) was also developed for wellbore cleanup;however, it can also be used to improve oil recovery. The approximatewater content is about 20% in the surfactant composition coming in fromthe individual components. FIG. 2A shows the surfactant composition with20% water, and FIG. 2B shows the homogenous 3000 ppm polymer solutionwith surfactant in the brine after 3 minutes mixing at room temperature.This solution is clear at reservoir temperature (FIG. 2C).

TABLE 3 Surfactant Composition 2. Wt % Wt % in in diluted aqueousconcentrated surfactant-polymer- surfactant Component polymer solutioncomposition TDA-8PO-Sulfate 0.15 4.8 C20-28 Isomerized olefin sulfonate0.3 9.6 C16-18 Isomerized olefin sulfonate 0.15 4.8 Sodium DihexylSulfosuccinate 0.5 16 Ethylene glycol monobutyl ether 0.75 24 Polymer0.3 8 Other (Water or brine, oil from polymer 97.85 32.8 and any othercomponents that conic with chemicals)

Surfactant Composition 3

This formulation (Table 4) was mainly developed to improve oil recovery.The approximate water content is about 8% in the surfactant composition(shown in FIG. 3A) coming in from the individual components. A largehydrophobe surfactant is used in this formulation to increase thesolubility. FIG. 3B shows that a homogenous 2500 ppm aqueoussurfactant-polymer solution can be obtained after mixing with brine for3 minutes at room temperature. This solution is clear at reservoirtemperature FIG. 3C.

TABLE 4 Surfactant Composition 3. Wt % Wt % in in diluted aqueousconcentrated surfactant-polymer- surfactant Component polymer solutioncomposition C28-35PO-10EO-Carboxylate 0.15 4 C20-28 Isomerized olefinsulfonate 0.05 1.35 C20-24 Isomerized olefin sulfonate 0.45 12.2 SodiumDihexyl Sulfosuccinate 0.5 13.57 Tri-ethylene glycol monobutyl ether0.75 20.36 Polymer 0.25 6.79 Other (Water or brine, oil from 97.85 41.73polymer and any other components that comes with chemicals)

Surfactant Composition 4

This formulation (Table 5) was developed to be used along withconventional slick water in hydraulic fracturing applications. Theconcentrated surfactant composition was made and diluted in slick water.The resulting aqueous surfactant-polymer solution include 0.6%surfactants and 0.03% polymer. FIG. 4A shows the surfactant compositionprior to dilution and FIG. 4B shows the slick water (the aqueoussurfactant-polymer solution) prepared by dilution of surfactantcomposition 4.

TABLE 5 Surfactant Composition 4. Wt % Wt % in in diluted aqueousconcentrated surfactant-polymer- surfactant Component polymer solutioncomposition C9-11 ethoxylated alcohol 0.5 64 benzenesulfonic acid, 0.113 decyl(Sulfophenoxy)-disodium salt Polymer 0.03 4 Other (Water orbrine, oil from 99.37 19 polymer and any other components that comeswith chemicals)

Evaluation of Surfactant Compositions

In general, there is a window for aqueous stability in terms of polymerconcentration in the aqueous surfactant-polymer solutions obtained fromthe surfactant compositions described herein. This window is dependenton the ratios of the various components mixed to make the surfactantcomposition, and can be adjusted by modifying the ratio and type of theindividual components that make up the surfactant compositions. Forinitial evaluation, dilutions were made in the laboratory with anoverhead stirrer for a specific time period.

All the data described below are based on surfactant composition 1 andthe resulting aqueous surfactant-polymer solution prepared by dilutingsurfactant composition 1 (as shown in Table 2. FIG. 5 shows a comparisonof the viscosity of surfactant composition 1 and the liquid polymer (LP)composition present in the surfactant composition. As shown in FIG. 5 ,the viscosity of the surfactant composition is lower due to the dilutionof the polymer activity. However, the composition exhibits a similarshear thinning viscosity profile to the liquid polymer.

FIG. 6 shows the viscosity curves as a function of shear rate atreservoir temperature for three different aqueous surfactant-polymersolutions having different concentrations of polymer prepared bydilution of surfactant composition 1. As shown in FIG. 6 , the presenceof surfactants or co-solvents do not impact polymer hydration and thecorresponding viscosity yields, as all the curves have traditional shearthinning behavior of diluted polymer solutions.

Table 6 shows the filterability and viscosity summary through a 1.2micron filter.

TABLE 6 Filterability and viscosity summary of the different aqueoussurfactant-polymer solutions (having varying polymer concentrations)prepared by dilution of surfactant composition 1 in brine. Polymerconcentration 1.2 μm filter Viscosity (cP) @ in the aqueous (15 psi, 25°C.) reservoir surfactant-polymer solution Time to temperature (ppm) F.R200 g (min) 10 s⁻¹ 3000 1.17 12 51 3000 1.24 21 56 3000 1.18 27 54 20001.3 26 24

As shown in Table 6, the aqueous surfactant-polymer solutions exhibitgood filterability at different concentration of polymer, indicatingthat the presence of surfactants and co-solvents in the aqueoussurfactant-polymer solutions does not negatively impact the filterratio.

FIG. 7 shows the oil recovery plot when aqueous surfactant-polymersolutions prepared from surfactant composition 1 (2500 ppm dilution)with a viscosity of ˜40 CP at 10 s⁻¹ and reservoir temperature wasinjected into surrogate rock (2″ diameter×12″ long Bentheimer with apermeability of 2.5 D) to displace ˜90 cP viscous oil. The core wasinitially saturated with oil and then brought to residual oil conditionsafter a tertiary polymer flood. The residual oil saturation was approx.30%. As shown in FIG. 7 , the residual oil recovered is 95% with theremaining oil saturation at the end of the chemical flood <2% in 2PV ofcleanup solution injection. This flood mimics a near wellbore cleanupsituation where trapped residual oil is mobilized by a continuoussurfactant-polymer solution injection. As a result of the displacementof the residual oil from the core, the relative permeability of the rockto the aqueous phase (krw) increases to 0.94, indicating the improvementin injectivity as seen in FIG. 8 .

FIG. 9 shows the recovery plot when 3000 ppm cleanup solution wasinjected to displace residual oil in a reservoir sand pack. Theviscosity of the injection solution was ˜55 cP at 10 s⁻¹ and reservoirtemperature. The residual oil saturation was approximately 17% beforeinjection of the aqueous surfactant-polymer solution with the same 90 cPviscous oil. The oil saturation at the end of the cleanup was <1% withoil recovery of approx. 99%. As a result of the displacement of theresidual oil from the sand, the relative permeability of the rock to theaqueous phase (krw) increases to almost 1, indicating the improvement ininfectivity as seen in FIG. 10 . FIG. 11 shows the visual appearance ofthe sandpack at the end of PF and at the end of the cleanup flood. Asshown in FIG. 11 , all of the residual oil has been displaced at the endof the flood, as indicated by the clean appearance of the sand.

Table 7 show the summary of the runs and the related observations aftersurfactant composition 1 was mixed inline using 2″ and 3″ size staticmixers with synthetic brine at predefined velocities and flowrates thatcorresponds to expected operating ranges in the field. As shown in Table7, three different polymer concentrations were mixed at the differentflowrates shown. The results indicate that the sufficient viscositiesare generated as seen from the viscosities for the differentconcentrations indicating the polymer in the surfactant composition isinverting, hydrating quickly to develop the viscosities in the presenceof the surfactants. Based on the polymer to surfactant and co-solventratios, the 2500 ppm aqueous surfactant-polymer solutions should becloudy or aqueously unstable which is what is observed. Also, there isone 3000 ppm solution which is cloudy possibly an outlier but themajority of the runs provide solutions with good viscosities andclarity.

TABLE 7 Summary of inline dilution using 2″ and 3″ static mixers forfield mixing scaleup. Polymer Viscosity concentration @ 10 s⁻¹ in theaqueous (cP), Pressure Clarity at surfactant-polymer reservoir Mixerdrop across Brine Velocity reservoir Run# solution (ppm) temp sizemixer(psi) (GPM) (m/s) temp 2A2 3000 72 2″ 9.6 33.4 1 Clear 2B2 300061.3 2″ 75 99 2.9 Clear 3A2 3000 51 3″ 3.2 69.3 0.9 Cloudy 3A3 3500 703″ 3.2 69.3 0.9 Clear 2A3 3500 91 2″ 9.6 33.3 1 Clear 2B1 2500 41 2″ 7299.3 2.9 cloudy 2A2 3000 85 2″ 9.5 33.4 1 Clear 2B1 2500 43.4 2″ 75 99.42.9 cloudy 2A1 2500 51 2″ 9.6 33.4 1 Clear

Table 8 shows the filterability summary of some of the runs described inTable 7. As shown in Table 8, all of the filter ratios (F.R) measuredwere less than 1.5. All the solutions were prefiltered through 5 μmfilter to remove any particles and contaminants that were present in thesynthetic brine.

TABLE 8 Filterability summary of some runs using the 2″ and 3″ staticmixers Polymer concentration 1.2 μm filter in the aqueous (15 psi, 25°C.) surfactant-polymer solution Time to 200 (ppm) F.R g (min) Run# 30001.04 48 2b2 3000 1.0 50 3a3 3000 1.12 73 7a2 2500 1.14 43 2b1 3000 1.0745 3a2 2500 1.03 29 2b1

The first coreflood recovery plot of residual oil in surrogate rock isshown in FIG. 12 using an aqueous surfactant-polymer solution collectedfrom the inline mixing test. The displacement was carried out using anaqueous surfactant-polymer solution obtained from run #2b2 (which had apolymer concentration of 3000 ppm and a viscosity of approx. 51 cP @10s⁻¹ and reservoir temperature). As shown in FIG. 12 , the final recoveryof residual oil is approx. 95% with the remaining oil saturation <2%.FIG. 13 shows the pressure drop during this recovery flood and thecorresponding improvement in the final krw which is >0.9, indicating theimprovement in krw at the end of 2 PV's of continuous injection of thecleanup solution.

FIGS. 14 and 15 show the oil recovery plot and the dp and krw plot when3000 ppm cleanup solution was injected to displace residual oil with thesolution used from run #3a2. Although the aqueous stability wassatisfactory due to the solution being cloudy, the total recovery isapprox. 97.5%, with the remaining oil saturation <1% as shown in FIG. 14. The pressure drop during this flood and the corresponding improvementin krw (>0.9) is shown in FIG. 15 . From the above two floods, one cansee that with inline diluted and mixed cleanup solution, the recoveryefficiency is still good.

The compositions and methods of the appended claims are not limited inscope by the specific compositions and methods described herein, whichare intended as illustrations of a few aspects of the claims. Anycompositions and methods that are functionally equivalent are intendedto fall within the scope of the claims. Various modifications of thecompositions and methods in addition to those shown and described hereinare intended to fall within the scope of the appended claims. Further,while only certain representative compositions and method stepsdisclosed herein are specifically described, other combinations of thecompositions and method steps also are intended to fall within the scopeof the appended claims, even if not specifically recited. Thus, acombination of steps, elements, components, or constituents may beexplicitly mentioned herein or less, however, other combinations ofsteps, elements, components, and constituents are included, even thoughnot explicitly stated.

The term “comprising” and variations thereof as used herein is usedsynonymously with the term “including” and variations thereof and areopen, non-limiting terms. Although the terms “comprising” and“including” have been used herein to describe various embodiments, theterms “consisting essentially of” and “consisting of” can be used inplace of “comprising” and “including” to provide for more specificembodiments of the invention and are also disclosed. Other than wherenoted, all numbers expressing geometries, dimensions, and so forth usedin the specification and claims are to be understood at the very least,and not as an attempt to limit the application of the doctrine ofequivalents to the scope of the claims, to be construed in light of thenumber of significant digits and ordinary rounding approaches.

It is understood that when combinations, subsets, groups, etc. ofelements are disclosed (e.g., combinations of components in acomposition, or combinations of steps in a method), that while specificreference of each of the various individual and collective combinationsand permutations of these elements may not be explicitly disclosed, eachis specifically contemplated and described herein. By way of example, ifa composition is described herein as including a component of type A, acomponent of type B, a component of type C, or any combination thereof,it is understood that this phrase describes all of the variousindividual and collective combinations and permutations of thesecomponents. For example, in some embodiments, the composition describedby this phrase could include only a component of type A. In someembodiments, the composition described by this phrase could include onlya component of type B. In some embodiments, the composition described bythis phrase could include only a component of type C. In someembodiments, the composition described by this phrase could include acomponent of type A and a component of type B. In some embodiments, thecomposition described by this phrase could include a component of type Aand a component of type C. In some embodiments, the compositiondescribed by this phrase could include a component of type B and acomponent of type C. In some embodiments, the composition described bythis phrase could include a component of type A, a component of type B,and a component of type C. In some embodiments, the compositiondescribed by this phrase could include two or more components of type A(e.g., A1 and A2). In some embodiments, the composition described bythis phrase could include two or more components of type B (e.g., B1 andB2). In some embodiments, the composition described by this phrase couldinclude two or more components of type C (e.g., C1 and C2), In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type A (A1and A2)), optionally one or more of a second component (e.g., optionallyone or more components of type B), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type B (B1and B2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type C). In someembodiments, the composition described by this phrase could include twoor more of a first component (e.g., two or more components of type C (C1and C2)), optionally one or more of a second component (e.g., optionallyone or more components of type A), and optionally one or more of a thirdcomponent (e.g., optionally one or more components of type B).

Unless defined otherwise, all technical and scientific terms used hereinhave the same meanings as commonly understood by one of skill in the artto which the disclosed invention belongs. Publications cited herein andthe materials for which they are cited are specifically, incorporated byreference.

What is claimed is:
 1. A method for performing an enhanced oil recovery(EOR) operation, comprising: (a) providing a subsurface reservoircontaining hydrocarbons therewithin; (b) providing a wellbore in fluidcommunication with the subsurface reservoir; (c) preparing an aqueoussurfactant-polymer solution; and (d) injecting the aqueoussurfactant-polymer solution through the wellbore into the subsurfacereservoir; wherein preparing an aqueous surfactant-polymer solution,comprises: providing a concentrated liquid surfactant compositioncomprising: (a) a surfactant package in an amount of from 0.2% to 98% byweight, based on the total weight of the concentrated liquid surfactantcomposition; (b) a co-solvent in an amount of from greater than 0% to95% by weight, based on the total weight of the concentrated liquidsurfactant composition; and (c) a liquid polymer (LP) composition in anamount of from 0.1% to 60% by weight, based on the total weight of theconcentrated liquid surfactant composition; wherein the concentratedliquid surfactant composition has a total water content of from 0.5% to20% by weight, based on the total weight of the concentrated liquidsurfactant composition; and combining the concentrated liquid surfactantcomposition with an aqueous fluid in a single stage mixing process toprovide the aqueous surfactant-polymer solution, wherein the singlestage mixing process comprises applying a specific mixing energy of atleast 0.10 kJ/kg to the concentrated liquid surfactant composition andthe aqueous fluid; and wherein the aqueous surfactant-polymer solutioncomprises a polymer concentration of from 50 to 15,000 ppm.
 2. Themethod of claim 1, wherein the wellbore in step (b) is an injectionwellbore associated with an injection well, and the method furthercomprises providing a production well spaced apart from the injectionwell a predetermined distance and having a production wellbore in fluidcommunication with the subsurface reservoir, wherein the injection ofthe aqueous surfactant-polymer solution in step (d) increases the flowof hydrocarbons to the production wellbore.
 3. The method of claim 2,wherein the method further comprises producing production fluid from theproduction well, the production fluid including at least a portion ofthe injected aqueous surfactant-polymer solution; and combining theproduction fluid with additional surfactant composition in a singlestage mixing process to provide a second aqueous surfactant-polymersolution.
 4. The method of claim 3, further comprising injecting thesecond aqueous surfactant-polymer solution into at least one injectionwell.
 5. The method of claim 1, wherein the subsurface reservoir is asubsea reservoir.
 6. The method of claim 1, wherein the subsurfacereservoir has a permeability of from 10 millidarcy to 40,000 millidarcy.7. The method of claim 1, wherein the aqueous surfactant-polymersolution is used as an injection fluid.
 8. The method of claim 1,wherein the aqueous surfactant-polymer solution is included in aninjection fluid.
 9. The method of claim 1, wherein the enhanced oilrecovery operation includes a polymer flooding operation, analkaline-polymer (AP) flooding operation, a surfactant-polymer (SP)flooding operation, an alkaline-surfactant-polymer flooding operation, aconformance control operation, or any combination thereof.
 10. Themethod of claim 1, wherein the aqueous surfactant-polymer solutioninjected in step (d) functions as a drag reducer that reduces frictionduring injection in step (d).
 11. The method of claim 1, wherein thesurfactant composition has a total additive concentration equal to thesum of the weight percent concentration of all surfactants and allco-solvents present in the surfactant composition; wherein thesurfactant composition has a total polymer concentration equal to thesum of the weight percent concentration of all polymers present in thesurfactant composition; and wherein the weight ratio of the totaladditive concentration to the total polymer concentration is at least1:1.
 12. The method of claim 1, wherein the surfactant package comprisesa primary surfactant and one or more secondary co-surfactants.
 13. Themethod of claim 1, wherein the LP composition comprises: a hydrophobicliquid having a boiling point at least 100° C.; at least 39% by weightof the synthetic (co)polymer; an emulsifier surfactant; and an invertingsurfactant.
 14. The method of claim 1, wherein the LP compositioncomprises an inverse emulsion comprising: a hydrophobic liquid having aboiling point at least 100° C.; up to 38% by weight of the synthetic(co)polymer; an emulsifier surfactant; and an inverting surfactant. 15.The method of claim 1, wherein the LP composition has a filter ratio of1.5 or less at 15 psi using a 1.2 μm filter.
 16. The method of claim 1,wherein the surfactant composition comprises an alkyl aryl sulfonatesurfactant.